History of Physics / Readings from Physics Today. Number Two

SPENCER R. WEART & MELBA PHILLIPS, EDITORS

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READINGS FROM PHYSICS TC

PUBLISHED BY THE

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HISTORY
OF PHYSICS

THE AMERICAN INSTITUTE OF PHYSICS is a not-for-profit membership corpora-
tion chartered in New York State in 1931 for the purpose of promoting the advancement
and diffusion of the knowledge of physics and its application to human welfare. Leading
societies in the field of physics and astronomy are its members. AIP’s activities include
providing services to its Member Societies in the publishing, fiscal, and educational
areas, as well as other services which can best be performed by one operating agency
rather than dispersed among the constituent societies.

Member Societies arrange for scientific meetings at which information on the latest
advances in physics is exchanged. They also ensure that high standards are maintained
in the publication of the results of scientific research. AIP has general responsibility for
the publication and distribution of journals. The Institute is expected to stay in the
forefront of publishing technology and to ensure that the services it performs for its
Member Societies are efficient, reliable, and economical.

The Institute publishes its own scientific journals as well as those of its Member
Societies; provides abstracting and indexing services; serves the public by making avail-
able to the press and other channels of public information reliable communications on
physics and astronomy; carries on extensive manpower activities; encourages and as-
sists in the documentation and study of the history and philosophy of physics; cooperates
with local, national and international organizations devoted to physics and related sci-
ences; and fosters the relations of physics to other sciences and to the arts and industry.

The scientists represented by the Institute through its Member Societies number
more than 60,000. In addition, approximately 7000 students in over 500 colleges and
universities are members of the Institute’s Society of Physics Students, which includes
the honor society Sigma Pi Sigma. Industry is represented through some 115 Corporate
Associate members.

AIP Officers:

Norman F. Ramsey, Chairman
H. William Koch, Director
Roderick M. Grant, Secretary
Gerald F. Gilbert, Treasurer

Lewis Slack, Associate Director for Educational Services
Robert H. Marks, Associate Director for Publishing

Edited by
Spencer R. Weart

Center for History of Physics
American Institute of Physics

and

Melba Phillips

Emeritus Professor of Physics
University of Chicago

Readings from Physics Today

Number Two

American Institute of Physics

New York, New York

1985

Readings from Physics Today

physics today, a publication of the American Institute of Physics, provides news cover-
age of national and international research activities in physics as well as government
and institutional activities that affect physics. Both technical and nontechnical develop-
ments are covered by scientific articles, news, stories, book reviews, letters to the editor,
calendars of meetings, and editorial opinion.

Articles in physics today are intended to be of interest to — and understandable by — a
broad audience of professionals from all subfields of physics as well as people with a
general interest in physical science.

History of Physics is the second book in a series of volumes that contains reprinted
articles and news material from physics today in other areas and subfields of physics.

Cover and title design by Charles Grenner

Copyright © 1985 American Institute of Physics 335 East 45th Street, NY, NY 10017

Individual readers of this volume and non-profit libraries, acting for them, are permit-
ted to make fair use of the material in it, such as copying an article for use in teaching or
research. Permission is granted to quote from this volume in scientific work with the
customary acknowledgment of the source. Republication or systematic or multiple re-
production of any material in this volume is permitted only under license from AIP.
Address inquiries to Office of Rights and Permissions, AIP.

Printed in the United States of America Pub. No. R-315.1

Library of Congress Catalog Card No. 85-70236

ISBN 0-88318-468-0

Introduction

physics today began publication in 1948, and for the first sever-
al years it contained no articles dealing with history of physics.
There was nothing remarkable in this, for one would have had to
look hard to find anywhere a journal article or a book dealing with
history of physics. The chief exceptions to this rule were occa-
sional scholarly studies of great early figures such as Galileo and
Newton. The historical map of more recent times was mostly
blank space, decorated here and there with prodigious figures
(Maxwell, Kelvin, Planck,...) known less through direct investiga-
tion than through anecdotes that grew in the retelling, like the
travellers' tales that populated early geographers’ maps with ti-
gers and sea serpents.

Historians did not notice that they lacked a history of mod-
ern science. Scholars who were not dedicated to the old narrow
history of “kings and battles” were leaping to a history of people
en masse : if presidents were not the key actors, then it must be
labor unions or corporations. Yet evidence was accumulating that
the center of modern history might lie somewhere between the
leaders and the masses, and perhaps even in laboratories. Many
would acknowledge that science had come to play a central role in
the development of society, but few scholars investigated the
question. To students of history, Einstein’s and Schrodinger’s
equations seemed far more obscure than any medieval Latin
parchment. As for the new generation of students of physics, they
had little time to spare for literature, and were mostly satisfied
with whatever colorful anecdotes they happened to hear about the
past of their discipline.

Interest in history began among leading physicists

It was left to older physicists to notice that something impor-
tant was being overlooked. Trained in the early decades of the
century by professors who perhaps remained unconvinced of the
value of relativity theory, these men and women had been young
when quantum mechanics burst upon the scene. They had seen a
mighty and complex intellectual process shake and transform
physics in a way that no generation had known for centuries.
Then, through the Great Depression, the Second World War, and
the Cold War, they saw the physics community itself reshaped
into a new form, while historical forces pulled physicists from
their laboratories and placed them under the spotlights of the
public stage — sometimes literally under spotlights. The older
physicists wanted to understand what they had lived through.
And they particularly wanted the next generation to understand
this history, so that the physics community might brace itself to
withstand and profit from the equally great transformations that
might be expected at any time.

In 1952 physics today carried its first two historical pieces,
both reprinted in this book: an article by Karl T. Compton on the
founding of the American Institute of Physics during the Depres-
sion, and an article by Edward U. Condon on the postwar rela-
tions between science and the federal government. Both men had
been at the very center of the events they recounted, but they were
not simply reminiscing about old times. Their articles carried les-
sons— which to this day are worth close attention — not only

about how the American physics community acquired its present
shape, but also about how in their opinion the community ought
to be shaped.

Meanwhile efforts were underway to bring an improved un-
derstanding of the past into physics education. A historical view-
point is inevitably present in teaching, whether as explicit stories
about scientists of the past, or implicitly. Many teachers had long
recognized that teaching physics as an abstract and perfected in-
tellectual structure, without a history, implicitly gives a distorted
and perhaps even damaging picture of the nature of scientific
research. And some teachers found history helpful in teaching
physics concepts.1 Such interest in the educational value of his-
tory became more widespread after the Second World War, as
evidenced by symposia and, eventually, international confer-
ences.2 Physicists with a strong historical orientation, for exam-
ple, Gerald Holton and Stephen Brush, worked with other histor-
ians of science not only to develop materials that could bring
history into physics education, but also to make sure it was accu-
rate history and not unverified folk tales. As more twentieth-cen-
tury physics entered the curriculum, historical interest broadened
still further. It was particularly during the 1960s that this move-
ment took hold.

Professional history of physics rose in the 1960s

The feeling that the history of modern physics merited close
attention inspired a few younger physicists to gamble their careers
by turning from physics research to historical research. Senior
physicists came to their support, and an institutional base for the
research was gradually laid down. One important example of this
work was the Sources for History of Quantum Physics project,
launched in 1961 and led by Thomas S. Kuhn with the aid of
several eminent physicists and a major grant from the National
Science Foundation.1 The original impulse had come with the
realization that people like Einstein and Schrodinger, who would
be honored so long as science was remembered, had died before
anyone asked them for the full details of how they had made their
epochal discoveries; but it was not too late to ask others and even
to get their recollections down on tape. (As it happened, it was late
indeed for Niels Bohr, who died after only two of several planned
interview sessions.) In the course of the project the physicist-
historians realized that tape-recorded recollections would not be
enough to secure a complete and accurate history, and they set to
microfilming files of correspondence as well. The resulting collec-
tion of interviews and microfilms has already served as “raw
data” for a large number of scholars, and is used more frequently
every year. People would have attempted to study the history of
atomic and quantum physics even without this project, but the
past two decades have seen publications on this subject (some of
them included in this book) in a quantity, and on a level of accura-
cy, that would otherwise have been impossible.

At the same time as the Sources for History of Quantum
Physics project was getting underway, other eminent physicists
were working to create a more permanent institution. They were
particularly concerned by the fact that physics, or at least physics

after Newton, was simply not mentioned in history textbooks and
other standard sources of culture. In the Smithsonian Museum,
for example, physics was subsumed under “electrical engineer-
ing.” In 1960 the concern over this situation helped establish a
history program at the American Institute of Physics; in 1965 it
became a permanent Center for History of Physics. The AIP Cen-
ter has worked steadily to conduct oral history interviews and
preserve documents, and has also worked to make the history
known through projects such as preparation of exhibits and aid to
scholars visiting its Niels Bohr Library. Many of the more recent
articles in this book drew directly or indirectly upon the AIP
Center’s resources.

Such efforts within the borders of the physics community
were reinforced during the 1960s by an outside movement. All
around the United States and also to some extent overseas, histor-
ians of science and even entire history of science departments
grew up in the universities. This was part of a general wave of
university expansion and diversification, but it had a special rela-
tionship to physics. At many places, physicists played a role in
getting the new departments established, and history of physics
became by far the most popular specialty within the history of
science (possibly excepting the history of medicine, which has its
own unique traditions).

History of modern science largely the history of physics

Why was the history of modern science, so far as it has been
written down, largely the history of physics? Perhaps it was for
the same reasons that, ever since I. I. Rabi got together with
Dwight Eisenhower, nearly all of the Presidents’ science advisers
have been physicists. One reason might be that physics is a mas-
ter-key to all the twentieth-century sciences; another, that nu-
clear weaponry has made scientists and the public especially
watchful of physics; yet another, that physicists have often had
broader viewpoints than other technically oriented people, with
an interest in everything from music to social relations. Whatever
the causes, the result was a rising generation of professional his-
torians of physics.

In the pages of physics TODAY, occasional articles began to
appear recounting historical stories that had nothing to do with
the personal reminiscences of the author. The articles by E. Men-
doza and C. S. Smith, reprinted here, show that such writings
could be not only interesting but also sophisticated history based
on direct investigation of evidence, even though the authors were
primarily scientists rather than professionally trained historians.
In 1 967 appeared the first articles by historians of science, Martin
Klein and Lawrence Badash. Even these two, however, were orig-
inally trained as physicists and were employed in university phys-
ics departments. It was only in the late 1 960s and especially in the
1 970s that there came a significant number of people trained from
the outset as deeply in history as in modern physics, and hired
explicitly as historians of science; the first to appear in these pages
is Charles Weiner, then Director of the AIP Center for History of
Physics. Since the mid 1970s a number of articles by such people
have appeared in physics TODAY. The author of the most recent
article reprinted here, Robert Rosenberg, is trained as a mainline
historian more than as a specialist in science.

A continuing dialogue between scientists and historians

The new type of article did not displace, but added onto,
historical writings by full-time physicists. Leaders of the profes-
sion have continued to write articles based on their own exper-
ience— sometimes recounting their persona! struggles and discov-
eries, sometimes telling of figures they knew during their careers,
most often writing a combination of both. Some of these physi-

cists have taken a leaf from historians, gathering reminiscences
from colleagues and searching for documentary evidence, aspir-
ing to a high standard of scholarly accuracy. This points to a
remarkable characteristic of the history of physics, not only in the
pages of PHYSICS today but more generally: any scholar or gen-
eral reader who would pursue the subject will end up reading a
mixture of first-person reminiscences and retrospective historical
accounts, mixed together with no clear boundary dividing them.

This close relationship between the people who are studying
history of physics, and the people who are the subjects of that
study, has helped to mobilize continuing support for the work. In
the 1980s this support is stronger than ever. The number of full-
time professional historians of physics continues to increase,
while physicists themselves are more than ever writing historical
articles and books, cooperating in oral history interviews, and
aiding in the permanent preservation of correspondence and oth-
er valuable unpublished papers in archival repositories. Many
physicists give personal, cash support directly to the Friends of
the AIP Center for History of Physics. Through The American
Physical Society they support a Division of History of Physics,
created in 1980 and already gathering together more members
than some of the Society's older divisions; the Division is very
active in arranging sessions of historical papers at meetings and in
a number of other areas. Through government agencies such as
the National Science Foundation and the Department of Energy,
and through grants and donations by industrial corporations and
private foundations such as Bell Laboratories, IBM, and the
Sloan Foundation, physicists and their friends are supporting a
number of important projects. Examples are a project to publish
all of Einstein’s papers and correspondence; an American Insti-
tute of Physics study of preservation of historical documentation
at government-contract laboratories; an International Project in
the History of Solid State Physics; and a Laser History Project.

A sturdy institutional base guarantees the continuation of
such activities. To be sure, the years since 1970 have seen a severe
weakening in universities of many academic fields and particular-
ly the humanities, and this has affected all fields of history. Im-
portant history of science departments and groups have been
weakened or even disbanded. But outside or alongside the univer-
sities, American history of science as a whole has been strength-
ened in the past half-dozen years by the creation of new institu-
tions such as the Charles Babbage Institute for the History of
Information Processing, the IEEE Center for History of Electri-
cal Engineering, and the Center for History of Chemistry. Mod-
elled initially on the AIP Center for History of Physics but sup-
ported by their own respective disciplines, these centers not only
complement but reinforce work in the history of physics itself.
Meanwhile, at such places as the University of California, Berke-
ley, Office for History of Science and Technology, and the Smith-
sonian Institution, groups interested in the history of modern
physics have grown vigorously.

There remain some intellectual weaknesses that have been
present from the outset. Study of the history of modern physics
has concentrated overwhelmingly on the theories of relativity and
quantum mechanics, perhaps because of these theories’ philo-
sophical interest, and on nuclear physics, perhaps because of its
social implications. Other fields such as solid state physics, which
may be even more important in the long run of history, are only
recently beginning to attract intensive study. Another weakness is
that most historians, coming from a literary and theoretical tradi-
tion, have written far more about the history of theory than of
experiment. Yet another problem is that nothing has been written
about the history of physics in industry, except by the very few
historians who have themselves worked as physicists in industry.

These deficiencies are rarely made good in first-person accounts
by physicists, most of which also tend to center more on theory in
the universities than on experiments or industrial research.

Meanwhile, the history of physics that gets written is still
read mainly by people trained in physics. A few pioneering books,
museum exhibits, and public television programs have reached a
wider audience, so that general historians and the public at large
are beginning to appreciate some features of the rise of modern
physics — but only beginning. Much more research and writing
must be done before nonphysicists can get a good feeling for the
history of physics, both in its own right and as an integral part of
modern history as a whole.

PHYSICS TODAY articles give an overview

We reprint here a selection of articles from the American Institute
of Physics magazine PHYSICS today. The magazine, like the AIP
itself, was founded partly in hopes of providing common services
that would help keep the physics community, with its highly di-
verse interests, from suffering fragmentation into subdisciplines.
History articles, which are perhaps the most generally popular of
all the types published in the magazine, have served especially
well in binding the community together, if only by giving what
one physics student described as a feeling for the shared “lore and
traditions" of the discipline.

No sampler of writings could give a comprehensive picture
of the history of modern physics; such a comprehensive picture
has indeed never been attempted by any author. The articles re-
printed here are more like pieces of a mosaic, with much blank
space in between. Yet by looking over the scattered pieces the
reader can get an idea of the mosaic as a whole, that is, of what has
happened in physics over the past two or three generations. These
pieces by their very heterogeneity may give a truer impression
than could be found in a single synthetic work.

We have had space for less than half of the history articles
that were available, and anyone looking over back issues of PHYS-
ICS TODAY will find other articles of a quality as high as those
included here. Reasons of balance, no doubt somewhat arbitrary,
have dictated hard choices. Also not included here, but very use-
ful for historical purposes, are the physics today obituaries.
Through these writings the physics community maintains a tradi-
tion of respect for its past members, a tradition once shared by all
scientific disciplines but which most other fields have allowed to
lapse. Finally, the magazine’s staff-written news columns and
particularly its “Search and Discovery” section have always con-
tained much of interest. In articles such as Gloria Lubkin's annu-
al pieces on Nobel Prize winners, these columns contain as much
historical investigation as current journalism.

Different ways to read this book

We advise readers that a history collection like this one
should not be approached as you would approach a physics text-
book— not with that grim determination to read through from the
start until you reach the end of the book, or your patience, or the
semester. Read this book more as you would read a physics jour-
nal: skim the titles to find one that sounds interesting, dip into the
article to see if it is appropriate to your interests (there are pieces
here which are suitable for high school students, and others that
assume knowledge around the graduate student level), and then
read all or perhaps only parts of the article. The pieces can be read
in any order, although we have put them in a rough sequence by
way of offering suggestions.

Bear in mind that this book mixes together two types of his-
torical writing which should be read in different ways. The differ-
ence is a traditional one, noted, for example, in 1891 by the great
historian Frederick Jackson Turner. "The antiquarian,” he
wrote, “strives to bring back the past for the sake of the past; the
historian strives to show the present to itself by revealing its origin
from the past.” Turner was more concerned with lessons for the
present than with what he called the “dead past.”4 He and many
later historians have striven to find general rules that might guide
us — if only the famous rule that the one thing we learn from his-
tory is not to be surprised by anything that happens. Many of the
articles here do aim “to show the present to itself,” using histori-
cal evidence to uncover the patterns of human action that shaped
the physics community and that continue to shape it. The form of
a bird's wing can be understood only if you know the evolutionary
history of birds.

Much of the writing in these pages, however, has been done
“for the sake of the past.” One thing we have learned from histori-
cal and sociological studies of physicists is that most people in the
discipline work less for material rewards such as wealth or leisure,
which few scientists can expect, than for the privilege of putting
their life’s effort into an imperishable structure. Whether as dis-
coverer or teacher, the goal is to leave a part of oneself within the
ever-growing and immortal entity that is physics. Physicists are
therefore specially concerned that their discoveries be justly re-
membered, and that their colleagues and predecessors likewise be
remembered for what they did. Only through such a tradition of
memory can they feel themselves firmly placed in time, whether
past, present, or future. One purpose of reading and writing his-
tory is to confirm this sense of identity within the community.

History has important lessons for today

Yet even reminiscences designed as a simple memorial to
past events are at the same time lessons in the traditions of the
community. These lessons are aimed at the present: what the
great figures of older days did, the author may imply, we in our
own lives should emulate (or if the result was bad, avoid). The wise
reader will therefore inspect every writing, however much it
seems to stay in the past, for the advice it may imply; historians
and sociologists will even use such writings as evidence for stan-
dards set up for scientific behavior. Of course, the wise reader will
also notice that articles which seem to analyze the past only in
order to reveal patterns of present concern, are reciprocally in-
vaded by an interest in the past for its own sake. Nobody can be a
good historian, or for that matter a good physicist, who does not
respect, as individuals in their own right and in their own times,
the people who laid the foundations for our present world.

1 . See Florian Cajori, "The Pedagogic Value of the History of Phys-
ics," School Rev., 278-285 (May 1899); Lloyd W. Taylor, Physics: The
Pioneer Science { Houghton Mifflin, Boston, 1941).

2. Symposia: “Use of Historical Material in Elementary and Ad-
vanced Instruction," Am. J. Phys. 18, 332 (1950); Proceedings of the Inter-
national Working Seminar on the Role of History of Physics in Physics
Education (University Press of New England, Hanover, NH, 1972).

3. Thomas S. Kuhn, John L. Heilbron, Paul Forman, and Lini Allen,
Sources for History of Quantum Physics. An Inventory and Report (Ameri-
can Philosophical Society, Philadelphia, 1967).

4. F. J. Turner, "The Significance of History,” The Varieties of His-
tory, edited by Fritz Stern (Vintage, New York, 1972), p. 201.

HISTORY OF PHYSICS

Edited by

Spencer R. Weart

Center for History of Physics
American Institute of Physics

Melba Phillips

Emeritus Professor of Physics
University of Chicago

Table of Contents

v INTRODUCTION
x Author Affiliations

1 CHAPTER 1: BEFORE OUR TIMES

2 The prehistory of solid-state physics Cyril Stanley Smith

12 Franklin’s physics John L. Heilbron

1 8 A sketch for a history of early thermodynamics E. Mendoza

I 25 A sketch for a history of the kinetic theory of gases E. Mendoza

29 Rowland’s physics John D. Miller

36 Michelson and his interferometer Robert S. Shankland

42 Poincare and cosmic evolution Stephen G. Brush

50 Steps toward the Hertzsprung-Russell Diagram David H. De Vorkin

59

61

68

74

78

86

94

CHAPTER 2: INSTITUTIONS OF PHYSICS

The roots of solid-state research at Bell Labs

Some personal experiences in the international coordination of
crystal diffractometry

The founding of the American Institute of Physics

The first fifty years of the AAPT

The giant cancer tube and the Kellogg Radiation Laboratory

The evolution of the Office of Naval Research

Lillian Hartmann Hoddeson

P. P. Ewald
Karl T. Compton
Melba Phillips
Charles H. Holbrow
The Bird Dogs

101 CHAPTER 3: SOCIAL CONTEXT

103 Nagaoka to Rutherford, 22 February 1911 Lawrence Badash

108 American physics and the origins of electrical engineering Robert Rosenberg

115 Physics in the Great Depression Charles Weiner

123 Scientists with a secret Spencer R. Weart

1 30 Some thoughts on science in the Federal government Edward U. Condon

138 Fifty years of physics education A. P. French

149 Women in physics: unnecessary, injurious and out of place? Vera Kistiakowsky

159 The last fifty years — A revolution? Spencer R. Weart

CHAPTER 4: BIOGRAPHY

The two Ernests

Van Vleck and magnetism

Alfred Lee Loomis — last great amateur of science
Harold Urey and the discovery of deuterium . .

Pyotr Kapitza, octogenarian dissident

The young Oppenheimer: Letters and recollections

Maria Goeppert Mayer — two-fold pioneer
Philip Morrison — A profile

Mark L. Oliphant
Philip W. Anderson
Luis W. Alvarez
Ferdinand G. Brickwedde
Grace Marmor Spruch
Alice Kimball Smith
and Charles Weiner
Robert G. Sachs
Anne Eisenberg

CHAPTER 5: PERSONAL ACCOUNTS

How I created the theory of relativity .
It might as well be spin

History of the cyclotron. Part I
History of the cyclotron. Part II
The discovery of fission

Physics at Columbia University

Albert Einstein
Samuel A. Goudsmit and
George E. Uhlenbeck
M. Stanley Livingston
Edwin M. McMillan
Otto R. Frisch and
John A. Wheeler
Enrico Fermi

CHAPTER 6: PARTICLES AND QUANTA

J. J. Thomson and the discovery of the electron . . .
Thermodynamics and quanta in Planck’s work . . . .

J. J. Thomson and the Bohr atom

Sixty years of quantum physics

Heisenberg and the early days of quantum mechanics

Electron diffraction: Fifty years ago

1932 — Moving into the new physics

The idea of the neutrino

The birth of elementary-particle physics

The discovery of electron tunneling into superconductors
The development of field theory in the last fifty years .

George P. Thomson
Martin J. Klein
John L. Heilbron
Edward U. Condon
Felix Bloch

Richard K. Gehrenbeck
Charles Weiner
Laurie M. Brown
Laurie M. Brown and

Lillian Hartmann Hoddeson
Roland W. Schmitt
Victor F. Weisskopf

Author Affiliations

Luis W. Alvarez, holder of the Nobel Prize in
Physics, is Emeritus Professor of Physics at the
University of California at Berkeley, (p. 198)

Philip W. Anderson, holder of the Nobel Prize
in Physics, has been a staff member of the
AT&T Bell Laboratories, and is professor of
physics at Princeton University, (p. 194)

Lawrence Badash is professor in the History
Department of the University of California at
Santa Barbara, (p. 103)

Felix Bloch (1905-1983), holder of the Nobel
Prize in Physics, taught in Zurich and Leipzig
and was professor of physics at Stanford
University, (p. 319)

Ferdinand G. Brickwedde is Evan Pugh
Research Professor of Physics Emeritus in the
Department of Physics at Penn State
University, University Park. (p. 208)

Laurie M. Brown is professor in the
Department of Physics and Astronomy at
Northwestern University, (pp. 340, 346)

Stephen G. Brush is professor in the
Department of History and the Institute for
Physical Science and Technology at the
University of Maryland at College Park. (p. 42)

Karl T. Compton (1887-1954) was a professor of
physics at Princeton University and then
President of the Massachusetts Institute of
Technology; he served on many important
boards and committees, (p. 74)

Edward U. Condon (1902-1974) taught physics
at Princeton and Washington University, St.
Louis; he was Associate Director of the
Westinghouse research laboratories, Director
of the National Bureau of Standards, and
Director of Research and Development for the
Corning Glass Works, (pp. 130, 310)

David H. DeVorkin is Chairman of the
Department of Space Science and Exploration
in the National Air and Space Museum of the
Smithsonian Institution, (p. 50)

Albert Einstein (1879-1955), holder of the
Nobel Prize in Physics, was professor of physics
at the University of Berlin and member of the
Institute for Advanced Study, Princeton,
(p. 243)

Anne Eisenberg teaches science writing at the
Polytechnic Institute of New York. (p. 234)

Paul P. Ewald, now in retirement in Ithaca,
New York, was professor of physics at Stuttgart
Polytechnic University, the Queen’s
University in Belfast, and the Polytechnic
Institute of Brooklyn, (p. 68)

Enrico Fermi (1901-1954), holder of the Nobel
Prize in Physics, was professor of physics at the
University of Rome, at Columbia University,
and at the University of Chicago, (p. 282)

Anthony P. French is professor in the
Department of Physics at the Massachusetts
Institute of Technology, (p. 138)

Otto R. Frisch (1904-1979) worked in
Germany, the Niels Bohr Institute in
Copenhagen, and in England, where he was
professor at the Cavendish Laboratory of
Cambridge University, (p. 272)

Richard K. Gehrenbeck is associate professor
in the Department of Physics and Astronomy of
the University of Rhode Island, (p. 324)

Samuel A. Goudsmit (1902-1978) studied at
Leiden University; he was professor of physics
at the University of Michigan, senior scientist
at Brookhaven National Laboratory, visiting
professor at the University of Nevada, and
editor of the Physical Review, (p. 246)

John L. Heilbron is professor in the
Department of History and Director of the
Office for History of Science and Technology of
the University of California at Berkeley,
(pp. 14, 303)

Lillian Hartmann Hoddeson is a member of the
Physics Department of the University of
Illinois at Urbana-Champaign and the
historian of physics at Fermilab. (pp. 61, 346)

Charles H. Holbrow is professor of physics and
Chairman of the Department of Physics and
Astronomy at Colgate University, (p. 86)

Vera Kistiakowsky is professor of physics at
the Massachusetts Institute of Technology,
(p. 149)

Martin J. Klein is Eugene Higgins Professor of
the History of Physics at Yale University,
(p. 294)

M. Stanley Livingston, now in retirement in
Santa Fe, was professor of physics at the
Massachusetts Institute of Technology, then
Director of the Cambridge Electron
Accelerator, and subsequently Associate
Director of the laboratory now called Fermilab.
(p. 255)

Edwin M. McMillan, holder of the Nobel Prize in
Physics, is former Director of the Lawrence
Berkeley Laboratory and Emeritus Professor
of Physics at the University of California at
Berkeley, (p. 261)

E. Mendoza has taught physics in the Physical
Laboratories of Manchester University,
England, (pp. 20, 25)

John D. Miller is professor of education at the
University of California in Berkeley, (p. 29)

Mark L. Oliphant, now in retirement in
Canberra, worked at the Cavendish Laboratory
and directed physics laboratories at the
University of Birmingham, England, and
subsequently at the Australian National
University, (p. 173)

Melba Phillips (editor), now in retirement in
New York City, is Emeritus Professor of
Physics at the University of Chicago, (p. 78)

Robert Rosenberg is a research associate in
the Edison papers project at Rutgers
University, (p. 108)

Robert G. Sachs is professor in the Physics
Department of the University of Chicago and
Director of the Enrico Fermi Institute there.

(p. 228)

Roland Schmitt is the General Electric
Company’s Senior Vice President for
Corporate Research and Development,
directing the GE Research and Development
Center in Schenectady, New York. (p. 354)

Robert S. Shankland (1908-1982) was Ambrose
Swasey Professor of Physics at Case Western
Reserve University, (p. 36)

Alice Kimball Smith is Dean Emeritus of the
Bunting Institute at Radcliffe College, (p. 221)

Cyril Stanley Smith is Institute Professor
Emeritus at the Massachusetts Institute of
Technology, (p. 2)

Grace Marmor Spruch is professor of physics at
Rutgers University, (p. 214)

George P. Thomson (1892-1975), son of J. J.
Thomson and holder of the Nobel Prize in
Physics, was professor at the University of
Aberdeen and the Imperial College of Science,
and Master of Corpus Christi College,
Cambridge, (p. 289)

George E. Uhienbeck studied at Leiden
University; he was professor of physics at the
University of Michigan and is Professor
Emeritus of Physics at the Rockefeller
University, New York. (p. 246)

Charles Weiner, former Director of the Center
for History of Physics at the American
Institute of Physics, is Professor of History of
Science and Technology in the Program in
Science, Technology, and Society at the
Massachusetts Institute of Technology,
(pp. 115, 221, 332)

Spencer R. Weart (editor) is Manager of the
Center for History of Physics at the American
Institute of Physics, (pp. 123, 159)

Victor F. Weisskopf, a former director of
CERN, is Institute Emeritus Professor of
Physics and Senior Lecturer at the
Massachusetts Institute of Technology, (p. 358)

John A. Wheeler is Ashbel Smith Professor and
Blumbert Professor of Physics and Director of
the Center for Theoretical Physics at the
University of Texas at Austin, (p. 272)

1

— Chapter 1

Ho tore Our Times

The main subject of PHYSICS TODAY is the subject declared
in the magazine's name, but we all recognize there is
much to learn from the past as well as from the immediate
present. For many people the past is simply what they
remember themselves, perhaps supplemented by what
acquaintances remember of their own lives. But since time
changes neither physical law nor human nature, there can
be an equal fascination in stories of events long vanished
from living memory. This section gives some of those
stories, arranged in roughly chronological order.

In various writings Cyril Stanley Smith has shown how,
long before science began, people were working to
appreciate the order of nature with both aesthetic
sensitivity and ingenious logic — a type of work that has
only become more important over the centuries. It was not
until the time of Galileo, however, that a few people began
to organize observations by means of laws whose validity
all serious thinkers could acknowledge. Great figures like
Galileo and Newton are the subject of numberless scholarly
articles and books, but our PHYSICS TODAY authors have
preferred to write about matters less familiar to the
average physicist. Some of the articles in this section,

especially the pair by E. Mendoza, summarize a broad area
with particular attention to correcting historical myths
that are still all too prevalent. The articles on Franklin and
Rowland go further, showing how mid eighteenth and late
nineteenth century "natural philosophers,” or at least
these particular two individuals, approached physics as a
whole — an intellectual enterprise with aims somewhat
different from what most physicists claim today.

The articles on Michelson, Poincare, and the
Hertzsprung-Russell Diagram take a still more focussed
approach. Each shows a particular scientific subject as it
developed over a few years or decades. The difficulties that
researchers encountered in each case are good examples of
the sort of problems all physicists and astronomers must
face, and it is worth noting how the problems were (or were
not) surmounted. It is also worth noting that in none of
these cases did science advance by the fully modern mode
with its extremes of hasty competition and teamwork.

Incidentally, these three articles are the only ones in this
book that deal with astronomy; articles on the history of
modern astronomy are included in the first volume of this
reprint series. Astrophysics Today.

Contents

2 The prehistory of solid-state physics Cyril Stanley Smith

12 Franklin’s physics John L. Heilbron

1 8 A sketch for a history of early thermodynamics E. Mendoza

25 A sketch for a history of the kinetic theory of gases E. Mendoza

29 Rowland’s physics John D. Miller

36 Michelson and his interferometer Robert S. Shankland

42 Poincare and cosmic evolution Stephen G. Brush

50 Steps toward the Hertzsprung-Russell Diagram David H. DeVorkin

2

HISTORY OF PHYSICS

The prehistory of

SOLID-STATE PHYSICS

PHYSICS TODAY / DECEMBER 1965

Introduction

Prehistory implies the selection of a date when
history begins. In solid-state physics this is very
recent, dating, perhaps, from Debye's specific-heat
theory of 1913, but most of all from the famous
diffraction experiment of Friedrich, Knipping, and
Von Laue in March 1912. It was this tool of
perfection which laid the ground for imperfection
to become of interest to physicists. The growth
of solid-state physics marks, I think, a basic change
in the attitude of physicists toward matter. Virtu-
ally all the development of mechanics, marvellous
though it was, was based on a treatment of matter
that was essentially structureless and whose meas-
ured elastic constants and densities gave the con-
stants to put into equations that became ever
more elaborate. When physicists at last paid atten-
tion to the structure of real crystals, they soon
became aware of imperfections, both theoretically
and experimentally, and the great flourishing of
solid-state physics in the last three decades has
been mostly based on the elucidation of the role
of mechanical, ionic, and electrical imperfections
in a crystal, accompanied, of course, by a continued
development of understanding of bonding and
dynamics of the ideal lattice.

There would be no physics at all if it were not
possible to find models ideal enough to compute
and sufficiently close to reality to be meaningful:
this has meant selecting areas of study one after
another in which this approach would be most
fruitful at a given time and ignoring others. It is
nevertheless interesting to read nineteenth-century
treatises on physics, whether research papers or

Cyril Stanley Smith is Institute Professor at the Massachu-
setts Institute of Technology. His article is based on a lec-
ture at the meeting of the American Physical Society in
New York on January 29, 1965, which began by the author’s
remarking: “Those who know me will suspect that the
title is a disguise for a talk on the history of metallurgy.
They will He partly right, though a subtitle might be The
interplay of mathematics and aesthetic empiricism in science.
If here I overemphasize empiricism, it is because I am
talking to physicists— a talk to practical metallurgists would,
conversely, overemphasize the value of mathematical theory.”

By Cyril Stanley Smith

textbooks, and to note the avoidance of the real
structure of matter. Despite the development of
good crystallography early in the nineteenth cen-
tury and despite the development of an essentially
valid ball-stacking model of ionic crystals as early
as 1812, virtually all nineteenth-century physics,
when it dealt with any structural concepts at all,
was based on the molecule. This is not, perhaps,
surprising, since the molecule had such a magnifi-
cent quantitative success in the kinetic theory of
gases and in explaining the composition of chemi-
cal compounds. (It is notable, however, that chem-
ists studied only those compounds that fitted the
theory, and Bertholet and others who insisted that
analyses frequently did not agree with the law of
simple multiple proportions were ignored.) Then
Cauchy’s model of crystal elasticity based on a
simple lattice failed to agree with measurement,
and all crystalline properties were referred to the
anisotropy of the molecule as a unit, not to the
arrangement of the units. Von Laue remarks in
his History of Physics that “no physical phenome-
non [of the nineteenth century] required the ac-
ceptance of the space lattice hypothesis.” I think
he should rather have said that physicists refused
to accept the concept, for the phenomena them-
selves certainly depended on lattices, while physi-
cists overexploited the adjustable flexibility of the
molecule to explain all anisotropic behavior,
whether optical, thermal, elastic, or electrical. Per-
haps the most revealing index of this blindness
is that the great Von Laue himself, a month be-
fore he had the epoch-making idea of the diffrac-
tion of x-rays from the three-dimensional crystal
grating, had to be told by a graduate student
that some people supposed that atoms might be
arranged in a regular array in a crystal. It was a
measure of his greatness how quickly he saw the
significance of the relationship to his theory of
crossed optical gratings; and it is a measure of
greatness again, and of the times, that the graduate
student, Paul Ewald, went on to write the first
text intended for physicists in which the properties

BEFORE OUR TIMES

3

of matter are realistically discussed on the basis
of their real structural and mechanical behavior.
This was his section in the eleventh edition of
Muller and Pouillet’s Lehrbuch dcr Physik, written
in 1927-28. Ewald drew heavily upon the experi-
mental work of Mark, Polanyi, and Schmid, on the
metallurgist’s study of grain growth and the
properties of single crystals. It was symptomatic
that this was an edited book with chapters by
different specialists.

There is something about the very nature of
physics itself that has produced this late develop-
ment: one cannot simultaneously have two views
of the world, a broad and a narrow one. Per-
haps, indeed, physics could turn to real solids only
after some centuries of concern with simple me-
chanics, and perhaps solid-state physics could only
result from a fusion of two streams of knowledge
which had to have time for development in isola-
tion before they impinged on each other with ex-
citing results. In the seventeenth century, when
qualitative speculation was still permitted, a natu-
ral philosopher could enjoy the diversity of prop-
erties of solids, which were explained in terms
of the interaction of imaginary corpuscles or parts;
rigorous physics following Newton quite rightly
discouraged such speculation, but unfortunately
the discouragement served also to exclude any in-
terest in the phenomena.*

However, concern with the real behavior of mat-
ter, if not a physicist’s characteristic, is certainly
a human one. The evolutionary advantage that
accompanied the ability to exploit the cracking of
stone gave rise to man himself. Studies, or perhaps
I should say enjoyment, of the plasticity, crys-
tallization, and vitrification of silicates and the
selective absorption of certain wavelengths of
light by metallic ions in an appropriate environ-
ment gave rise to the magnificent art of ceramics.
The making of jewelry, tools, and weapons in-
volved knowledge, if not atomistic understanding,
of virtually every property now being studied by
physicists except electrical conductivity and the
effects of irradiation. There is something about
man’s relationship to matter through his senses

*1 don’t wish to accuse physicists of being particularly per-
verse in refusing to look at crystals. The most recently pub-
lished history of the constitution of matter bears the
promising title, The Architecture of Matter, hut it is con-
cerned almost entirely with atomic and subatomic concepts.
Even historians seem to be unable to sec beyond atomic or
molecular bricks to the magnificently diverse structures that
are composed of them, unless they go the whole hog and
study cosmology at the other end of the scale, equally in-
tangible and so equally capable of being oversimplified for
the purpose of thought.

that inspired him to experiment empirically with
the effect of heat on natural substances, singly
and in mixture, at the same time that he was
experimenting with social organization and long
before he began to develop the more intellectual
mechanical arts. Virtually not until the twentieth
century did the engineer outstrip the materials
that had been discovered 4000 years earlier; and
progress in metallurgy had been mostly that of
making more of the old metals and alloys more
cheaply.1 Thanks largely to recent discoveries of
physics— at first electricity and lately nuclear fis-
sion—the metallurgist is now forced to be more
qualitatively creative than he has been for many
centuries. I use the word “quality” intentionally,
for I believe that quality (in both of its meanings)
has inspired human advance far more than has
numerical quantity.

Philosophy— Aristotelian and corpuscular

Greek philosophy was much concerned with
qualities, culminating in Aristotle’s theories of
matter, in which the four elements carried the ele-
mental qualities— hot, cold, dry, and moist— in
various combinations in a body to give rise to
all of the properties that were perceptible to the
senses. These ideas dominated most thinking un-
til the seventeenth century, and most explanations
ol the nature of bodies lay in purely ad hoc sug-
gestions as to the relative amounts of the qualities,
with an ingeniousness but disregard for verifi-
ability that we find shocking today. Nevertheless,
it should be noticed that it is precisely the quali-
ties that concern the solid-state physicists that
were then regarded as central to understanding of
matter— conductivity, plasticity, fusibility, color,
texture, and hardness. The seventeeth century
saw the end of this. Physics— mathematical physics
in the pattern that was nucleated in the Middle
Ages, began to crystallize around Galileo, and
reached marvellous maturity with Newton-
changed all this, for qualities could not be calcu-
lated, and even when it became possible to measure
“properties” something had to be left out, every-
thing dependent on the interaction of many
parts. Mechanics and optics alone proved amen-
able to mathematical treatment.

Virtually every advance since the seventeenth
century has stemmed from the unwillingness of
the physicist to talk vaguely about things that
cannot be reduced to computable models whose
inaccuracies can be exposed and removed by con-
tinual interaction with experiment. Science is in
very essence both mathematical and experimental,
but at times one or the other viewpoint has grown

4

HISTORY OF PHYSICS

Drawing by Robert Hooke showing packing of spheres
to match polyhedral shapes in alum and salt crystals.
(Micrographia, London 1665). This drawing and illus-
trations on pages 21, 26, and 29 were taken from C. S.
Smith, A History of Metallography, Chicago 1965.

beyond balance. That most marvellous of physi-
cists, Robert Hooke, wrote in 1665: “. . . and here
the difficulty is . . . least by seeking to inlarge our
Knowledge, we should render it weak and un-
certain; and least by being too scrupulous and
exact about every Circumstance of it, we should
confine and streighten it too much.”

The idea that many properties were somehow
related to the interaction of smaller units of struc-
ture was developed by Democritus and other early
Greek thinkers and might have reached fruition
by interaction with the Pythagorean emphasis upon
form had they not been rejected by the most
authoritative Greek philosopher, Aristotle. How
different the history of science might have been had
he been an atomist, or had his work called forth
constructive criticism instead of adulation! Really
creative thinking occurred again only in late medi-
eval times after the revival of the forgotten
atomism. Marshall Clagett at the recent Montreal
meeting of the History of Science Society discussed
Nicholas Oresme’s remarkable fourteenth-century
ideas in which he makes the qualities themselves
depend on form. He says: ‘‘The ratio of intensi-
ties is not so properly or so easily attainable by
the senses as is the ratio of extensions,” and then
describes how to plot the intensity of a quality
normal to the extension of the substance, and dis-
cusses a kind of resonance between adjacent bodies
depending upon the conformity and difformity of
the arrangements of their representations in quali-
ty space. Remarking that experience and philoso-
phy alike show that all natural bodies determine
their shapes in themselves, he says they also de-
termine in themselves the qualities that are natural
to them, and that, “In addition to the shape that

these qualities possess in their subject, it is neces-
sary that they be figured with a figuration that they
possess from their intensity,” and, “It is necessary
that qualities of this sort have diverse powers and
action depending on the difference in figurations
previously described.” He does not quite go on to
describe a Brillouin-zone polyhedron, but his re-
marks on the mutually conformable configuration
of qualities in seeds would not startle a modern
biologist.

Oresme’s ideas were based on an intuitive feel-
ing for form. His realization that the intensity of a
quality could be plotted so as to make it appreciable
to the senses was a great inspiration, but it led
to no immediate development. Everyone knows of
the great developments of astronomy that occurred
in the sixteenth and seventeenth centuries; few
people have studied the equally interesting but
less fruitful studies on the properties of matter
that occurred at the same time, for the practical
consolidation of knowledge in this area was not
accompanied by a theory of the kind that could
become part of the mathematical mainstream of
science.

In the seventeenth century, natural philosophy
reached its prescientific height and this was the
last time for three centuries that respectable think-
ers concerned themselves with the properties of real
solids. Atomism, or at least corpuscular philosophy,
was invoked to explain everything; but the shape
of the parts, like the proportions of the preceding
Aristotelian qualities, were adjustable ad lib, and
could not be expressed in the soon-to-be-manda-
tory mathematical form or related to experiment.
Nevertheless, there are some seventeenth-century
writings that are entrancing for a twentieth-century
solid-state physicist to read. In a purely qualitative
way, physicists and philosophers deduced models
of behavior based upon shape, size, and interaction
of parts which (if we properly select for each occa-
sion the appropriate unit as an atom, molecule,
subgrain, microcrystal, or crystal) are qualitatively
as we would have them today. Molecules are formed
by parts of different shapes sticking together, and
metals are plastic because the parts can slide over
each other and change neighbors without losing
coherence. Descartes, who had watched wrought
iron coming to nature in the molten bath of a fiery
hearth, saw that there was something about parti-
cles on one scale which enabled them to be joined
into grains within which cohesion was greater than
with other grains, though oddly he failed to see
that the grains were crystalline. The most popular
Cartesian physicist, Rohault, in his Traite de
Physique (1671) , supposes that plastic materials are

BEFORE OUR TIMES

5

made of parts with complicated textures intermixed
with each other, hooked together like the rings of
a chain or entwined like the threads of a cord,
while brittle bodies are of simple texture with par-
ticles touching one another at only a few places.
He talks about the preferred orientation of par-
ticles after hammering or drawing, and the prefer-
ential clumping of particles into grosser particles
under the influence of heat, structures which in
steel can be preserved by quenching and are re-
sponsible for its hardness. Somewhat later (1722),
these ideas in the mind of the great Reaumur
led to the inversion of the ancient belief that
steel was a purified iron (logical enough, since
steel resulted from prolonged treatment in fire,
which does usually purify) and he suggested that
it arose from the addition of some particulate
matter (“sulfurs and salts”) which could be dis-
tributed or segregated by heat treatment within a
hierarchy of structures of iron particles with ac-
companying hardening or softening.

Another Cartesian physicist, Hartsoeker (1696),
let his imagination run wild. He cooked up all
kinds of amazing contraptions to explain the prop-
erties of matter. Corrosive sublimate becomes a
ball of mercury with, stuck all over it, particles
of salt and vitriol shaped like needles and cutting
blades; air is a hollow ball built of wirelike rings
to give it the necessary elasticity. He conjectured
that the particles of a substance like iron, which
is hard when cold but malleable when hot, must
have teeth which slide over each other when the
particles of heat have sufficiently separated them;
the parts of mercury, being spherical, can slide

Drawing by R. A. F. de Reaumur (1772) showing
“A grain of steel as it would look if it were vastly
enlarged. Its natural size is shown in G. MMM are
the molecules of which the grain is composed;
VV the voids left between them”. Reaumur ex-
plained the conversion of iron into steel by diffu-
sion into the iron of particles of reducing and
saline matter from the cementing compound. He
explained the hardening of steel by the redistribu-
tion of this matter between the grains and inter-
granular spaces. He had no concept that there was
crystalline order within the grains.

easily between polyhedral particles of gold (is not
this indeed the basis of liquid-metal embrittle-
ment?) and so on. After numerous specific examples
he ends, “But I do not wish to deprive the reader
of the pleasure of himself making the search fol-
lowing the principles that have been established
above.” It is precisely this element of uncontrolled
imagination in the speculation that made respecta-
ble physicists turn their back on this kind of think-
ing. Yet the particle, of course, usually without

Conjectural shapes of the particles of
matter according to the corpuscular phys-
icist Nicholas Hartsoeker (1696). The
spherical ball with attached spikes repre-
sents mercuric chloride; the toothed
pieces are iron, which is hard when cold
because the particles interlock, but is
easily forged when heat particles distend
the parts so that they can slide over
each other.

6

HISTORY OF PHYSICS

any such specific remarks as to its shape and pack-
ing, was accepted by virtually everyone after the
middle of the seventeenth century.2 As in so many
things, Newton provided (in the notes to the sec-
ond edition of his Op ticks [London: 1718]) a sum-
mary of a viewpoint beyond which it was unwise
to go:

There are therefore Agents in Nature able to make
the Particles of Bodies stick together by very strong
Attractions. And it is the Business of experimental
Philosophy to find them out.

Now the smallest Particles of Matter may cohere by
the strongest Attractions, and compose bigger Par-
ticles of weaker Virtue and many of these may co-
here and compose bigger Particles whose Virtue is
still weaker, and so on for divers Successions, until
the Progression end in the biggest Particles on
which the Operations in Chymistry, and the Col-
ours of natural Bodies depend, which by co-
hering compose Bodies of a sensible Magnitude. If
the Body is compact, and bends or yields inward to
Pression without any sliding of its Parts, it is hard
and elastick, returning to its Figure with a Force
arising from the mutual Attraction of its Parts. If
the Parts slide upon one another, the Body is mal-
leable or soft. If they slip easily, and are of a fit
Size to be agitated by Heat, and the Heat is big
enough to keep them in Agitation, the Body is
fluid. . . .

This is not the Newton of the Principia speaking,
but it was the Principia that set the tone for phys-
ics. Virtually all speculation on the nature of solids
disappears thereafter from the writings of good
physicists for two centuries. The physics of solids
was limited almost exclusively to idealized elastici-
ty, a favorite subject with mathematicians as well
as physicists, but one which, except for the mathe-
matical atomism of Boscovich, was divorced from
any concepts as to ultimate structure. This is not
to say that there were not speculations on the na-
ture of crystals and even some marvellous mathe-
matics of crystallography to which I will return
later, but both of these were outside the main-
stream of physics. But I wish to return to the
theme of qualities and take up another thread.

The alchemists

The nuclear physicist can laugh at the alchemist’s
misguided attempt at transmutation, hut the solid-
state physicist shouldn’t. Transmutation has not al-
ways had today’s connotation of a change in the
nucleus of an atom. Looked at qualitatively, the
change from a mixture of sand and ashes into
glass, from a mixture of malachite, calamine, and
charcoal into gleaming brass, or from a white
fabric into an Emperor’s purple robe is a most
spectacular and fundamental change. To Aristoteli-
ans, the whole difference between substances lies in

their particular combination of qualities, and since
it is clearly possible to produce some of these at
will, why not others? The modern materials engi-
neer is producing new qualities all the time, but
he does not call it transmutation.

As has been argued especially well by Hopkins
in his Alchemy, Child, of Greek Philosophy (1934),
alchemy began reasonably enough on the basis of
the well-known changes in color and nature which
had long been exploited by artisans for decorative
purposes in goldwork, in enamels and in dyeing.
It was supported by the belief that somehow be-
hind these changes there lay a key to the relation-
ships and transformations in the larger world (a
view that anyone with a spark of the artist in him
must admire) but it failed eventually simply be-
cause the adepts came to have too great a belief
in the premature theory, and they became too pre-
occupied in the observable qualities rather than
their compositional causes, and so were unable to
benefit from the innumerable experiments that
were done. If the yellow matter that came from
heating copper with certain substances was re-
garded as only an inferior gold, the experiment
was a failure: it could have been regarded as a
more castable, harder, and resplendent form of
useful copper. Yet what wonderful physical changes
the alchemists produced, and how fervently and
how rightly they believed in the significance of
the difference between the qualities of a shiny
ductile metal; a black, brittle sulfide; a crumbly
crystalline salt; gleaming, hard diamond; infusible
earths; and the vapors, phlegms, and tars that
came from distilling animal and vegetable matter.
These properties are the subject of solid-state
physics, but there were no solid-state physicists in
those days.

T he beauty of alchemical mysticism attracted ad-
herents long after it was obvious that it was not a
fruitful guide (obvious in retrospect, that is) . It
was slowly replaced by the belief that eventually
became the mainstream of chemistry that the quali-
ties were dependent upon composition and that
they were not dependent only on the units but also
sometimes on the manner of combination. At first,
however, the qualities needed an embodiment, and
perhaps largely under the influence of miners, mer-
cury and sulfur (the philosophical kinds, not the
ordinary materials) were thought to account for most
substances by their varied combination. Sulfur rep-
resented the inflammable principle, the soul, the
fire of Aristotle, while mercury was the materializa-
tion of the fluidity principle. Paracelsus early in
the sixteenth century methodized this viewpoint and
added a third principle, salt; he also directed chem-

An eighteenth-century metallurgical laboratory with apparatus for determining the physical and
chemical properties of metals. (William Lewis Commercium philosophico-technicum, London 1763)

istry toward a useful practical purpose, medicine,
and away from its domination by mystic philoso-
phy. Salt, sulfur, and mercury— excellent examples
of ionic, Van der Waals, and metallic bonding;
had diamond with its covalent bonding been
added, all types of today’s quantum theory of solids
would have been represented. The problem was
in the realm of solid-state physics, but there were
no solid-state physicists in those days.

No physicist arose to meet the challenge, but
chemists had to do something and so did practical
smelters and assayers of ore. The inflammable prin-
ciple, the reducing principle, the sulfur of Paracel-
sus, was supposed to be transferred from charcoal
to a metal ore when the latter was converted to
metal. It became the terra pinguis, the unctuous
earth of J. J. Becher in 1667, and was elevated to
that important chemical principle, phlogiston, by
J. H. Stahl, a metallurgical chemist, in 1703. Very
much of eighteenth-century chemistry revolved
around the phlogiston theory and the degree to
which this evanescent material was transferred
from one substance to another in reaction. But
the study of reactions was now being done sys-
tematically, and tables of affinity appeared— the
first in 1718— putting substances in order of their
affinity for each other, each being able to displace
those above it from compounds. Though phlogiston

had some of the chameleon-like variability of the
alchemist’s elusive elixir, it was responsible for
metallicity and its loss left a calx (an oxide in
today’s terminology). The presence of an excess
of it changed iron into steel, and still more into
cast iron. Parallel with the phlogiston studies went
an intensive study of the composition of matter,
sparked to some extent by the desire to duplicate
Chinese porcelain. The definition of element be-
came something that could not be chemically brok-
en down and it appeared that there were many
elements, though not an infinite number. Analyti-
cal chemistry evolved from the assayer’s ancient
technique of extracting the noble metals in weigh-
able metallic form, usually on the basis of in-
genious pyrochemical reactions, and became broad-
ly applicable when it was found in the eighteenth
century that compounds of definite composition
could be precipitated reproducibly by reaction in
aqueous solution and weighed. This was accom-
panied by a growing interest in the role of gases
and the rather sudden appreciation of the chemical
role of atmospheric oxygen, which quickly demol-
ished the phlogiston theory. The new chemical
nomenclature of Lavoisier and his associates tied to-
gether all of the analytical data into a clear listing
of the elements and their relationships in numer-
ous natural and artificial compounds, and there-

8

HISTORY OF PHYSICS

15. Depositing Arrangement No. 6.— Deposition ly Magnet and Coil (Fig. 14)

We may produce deposition in the separate liquid by connecting the two pieces of immersed
metal with any other source of depositing power— for instance, if a long copper wire A,
covered with silk or cotton, is coiled upon a large bar of pure soft iron B, and its ends
C and D are immersed in a solution of sulphate of copper E, and the poles of a
powerful horse-shoe magnet F are brought in contact very many times with the end
of the bar, and every time before removing the magnet from the bar one of the ends

of the wire is taken out
of the liquid, and re-
placed before returning
the magnet, one end of
the copper will slightly
dissolve, and the other
receive a thin copper de-

„ ,, . posit; but if each of the

ends is allowed to remain constantly in the liquid, no such effects will occur.

An early phlogiston pump (not so
named!). From G. Gore, Theory
and practice of Electrodeposition,

London 1856

after composition alone became the chemist’s ex-
planation for all of his phenomena. The chemist,
the mineralogist, and the metallurgist were still
almost the only people seriously interested in the
nature of solids.

Looked at from today’s viewpoint, it is obvious
that the phlogistonists were right. T he difference
in properties between black brittle cuprite and
shiny malleable copper is due to phlogiston: phlo-
giston is simply the valence electron in the conduc-
tion band of today’s quantum theory. The phlo-
gistonists did overlook the oxygen atom which
trapped the electron, and this is a pretty large
thing to overlook, but they were right physically if
not chemically. They had to use other atoms
(composition) to manipulate the phlogiston; today
we simply pump phlogiston through an electrolytic
cell, add it to ions, and get metal. A ton of
aluminum, it turns out, needs just about two
ounces of phlogiston for its preparation!

After the development of analytical chemistry in
the 1780’s, very many of the age-old properties
of metals and other materials were found to be
associated with specific compositions, and even very
minor amounts of impurities such as phosphorous
or sulfur in iron were found sometimes to be as-
sociated with great physical changes. One of the
first triumphs— again under inspiration from the
Orient, in this case in the form of the Damascus
sword— was the discovery that it was minute but
varying amounts of carbon, a real material sub-
stance now classed as an element, that was respon-
sible for the striking differences between wrought
iron, steel, and cast iron.

After this, composition per se was, for a time,
regarded as a sufficient explanation of the won-
drous diversity of properties of substances. Analy-
sis provided the basis for the classification of sub-
stances. After the atomic theory of Dalton (which
was no more of an atomic theory than had existed
for centuries but was a really fine quantitative the-
ory of simple molecules) chemists’ eyes were for a

long time closed to compounds that were not sim-
ple. The reactions of metallurgy, which largely in-
volve solid solutions, lost interest to the chemist,
who now worked mostly with ionic compounds or
aqueous solutions of them (or with organic mole-
cules) and interpreted the simple ratios of atoms
found by analysis as representing molecules. Su-
perb quantitative proof of the existence of mole-
cules was provided by the combining volumes of
gases and by the kinetic theory of their PVT rela-
tions, but most of the chemist’s precipitated com-
pounds were actually in simple ratios only because
of the geometric requirements of the crystal lattice.
Physicists were of no help. If nineteenth-century
physicists were interested in solids at all, they too
talked about the relations of the molecules, though
molecules were often supposed to be spatially ori-
ented (not on lattice points but sometimes within
unit cells) to account for the anisotropic properties
of crystals.

Crystallography

T he introduction of. the crystal makes me take an-
other leap back in time. Crystals initially were
simply bodies with a certain geometric external
shape, and quartz was the archetype. They were
brittle, commonly transparent.

There are few subjects better adapted to ele-
gant treatment by the mathematical physicist than
is crystallography, yet, although physical proper-
ties of crystals were often measured, crystallography
did not really become part of physics until after
x-ray diffraction. Nineteenth-century physicists
showed an almost incredible restraint in speculat-
ing on the details of the atomic, or as they would
call it, molecular, arrangements responsible for the
symmetrical anisotropy of the shapes and proper-
ties of crystalline matter. T he mineralogists, how-
ever, fairly early realized the value of crystal meas-
urement in the identification of minerals. Though
much had been done before, it was Linnaeus’ tie-
sire for classification in the realm of natural his-

BEFORE OUR TIMES

9

tory that gave the real impetus to the collection of
data on crystal faces and their angles, and the
seeking of a satisfactory model that would ex-
plain them in their diversity. The great Hairy who
was the first to develop the mathematics of the
angular relationships did this on the basis of an
earlier supposition that crystals were composed of
aggregates of tiny polyhedra (called integrant mole-
cules), with all faces that did not correspond to
the plane faces of the unit arising from the re-
moval of polyhedra in a simply stepped array of
building blocks. Incidentally, he remarks that the
similarity between different individual crystals of
the same species is less evident than the similarity
between different individuals of a biological spe-
cies—a view that we find astonishing today with
our mind on the perfect regularity of the space
lattice as the main characteristic.

The assembly of polyhedral parts to give cubic and
rhombohedral crystals (Grignon, Essai de Physique
sur le fer, Paris 1775). A model of this kind was
used by Haiiy as the basis of the first calculations
of the angles between crystal faces in 1784.

Models of crystal structures made by VV. H. Wollas-
ton in 1812. (Proceedings of the Royal Society, 1813)

Haiiy explicitly disclaims the possibility of know-
ing the ultimate structure of matter, though he
considered the structural units definitely to be poly-
hedra within which the molecular interactions
were different from those outside; it was a kind
of geometric package, and had been arrived at by
Haiiy as by others before him simply on the basis
of observations on the disparity between the cleav-
age and the growth faces of crystals. To our minds,
the stacking of balls seems to provide a more physi-
cally meaningful model of simple crystals, though
mathematically, of course, there need be no dif-
ference between the two. It is therefore particularly
interesting to see that the first thoughts about the
nature of crystals involved exactly this model. It
was suggested by Thomas Harriot about 1599
though first published by Kepler in 1611 and de-
veloped particularly by Hooke and Huygens later
in the seventeenth century. Hooke, for instance,
showed that all of the surfaces of alum crystals
could be matched by stacks of globular bullets
arranged in close packing, and he suggested that
sea salt is built of globules placed in a cubic
arrangement. He saw the relation of stacking to
the sixfold dendrite formation in snow, though
in characteristic Hookian fashion he merely out-
lined a program of study and did not follow it
through. Huygens used a similar model with sphe-
roids to explain the cleavage and optical proper-
ties of calcite, but after him the ball model dis-
appears, to be replaced with stacks of polyhedra.
Even more astonishing is the fact that when the
stacking-of-spheres model is resurrected by the
great Wollaston in 1812 and used to explain the
nature of several bodies, including the alternate
regular stacking of large and small spheres to ac-
count for rock salt, again it is rejected in favor of
Hariy’s approach. The polyhedra somehow seemed
to lend themselves more readily to mathematics,
and they were mathematically, though not physi-
cally, replaced somewhat later in the century by
the more ideal point-group model of the mathe-
matical crystallographers. Stacks of ball-shaped
atoms came back again in a paper by Barlow in
the 1 880’s — notice that it is the more pragmatic
approach of the English, not the elegant mathe-
matics of Continental physicists, that produced it.
It was being well developed by Barlow and Pope,
Sohncke and others, all of a chemical turn of
mind, when x-ray diffraction suddenly provided
the experimental handle to enable both the sym-
metry and the chemistry to be combined in a
properly scientific scheme. The first surprise, in-
deed it was a shock, was the realization that no
molecules existed in simple ionic crystals. The re-

10

HISTORY OF PHYSICS

lationship between the ball-like atoms and the
stacking polyhedra of the unit cell was thereafter
clear to every freshman. It is ironic that just as
the ball model was vindicated, the atom itself lost
all reality and we have now turned to the neat
polyhedra of the Brillouin zone as the most
reasonable model of the unit of the crystal. For
the first time, the model is one which is neither
a determining unit nor a dominating array, but
results from the two-way interaction between unit
and arrangement.

This brings me to the subject I am mainly in-
terested in, metallurgy, for nineteenth-century met-
allurgy is virtually a qualitative preparation for
twentieth-century solid-state physics. Here, for the
first time, the earlier qualitative speculation on the
relation between structure and properties begins
to take definite useful form. First, it was realized
that the essence of crystallinity lies in internal order
not in external form, and more important, that
most solid inorganic bodies are composed of hosts
of microcrystals. The knowledge that metals had a
granular texture, of course, goes back to the earfi-
est broken piece of metal, and the fracture test
was the principal basis of selection and quality con-
trol for millennia. In the eighteenth century,
Reaumur used experiments on fracture combined
with Cartesian corpuscular philosophy to give the
first good theory of steel, but it was not until the
middle of the nineteenth century that the granular
structure was experimentally shown to be micro-
crystalline. The nucleating observations occurred
appropriately enough in the steelmaking town of
Sheffield in England, almost exactly a hundred
years ago, when Henry Clifton Sorby, for the first
time in history, prepared the surface of a sample
of steel carefully enough so that the structure
could be seen under a microscope without the dis-
tortions that had rendered the structure invisible
to early microscopists. The background of Sorby’s
use of acid to develop the structure is itself an
interesting bit of history, for it has roots not only
in the artist’s etched prints and decoration of armor
but also in the oriental “Damascus” sword, the
etching of which led to the etching of meteorites.
Sorby saw that metals did not crystallize under
vibration— a long-lived myth— but were always
finely polycrystalline. He saw that they could be
distorted while maintaining crystallinity and would
recrystallize either as a resut of an allotropic
transformation as in steel, or simply on heating
after straining by cold work. He also identified
most of the phases now known in steel, but he
did not continue in the field very long, and it was
left to other workers who took up the subject

Print made directly from the etched and inked sur-
face of the Elbogen iron meteorite by Schriebers
and von Widmanstatten in 1813. Slightly enlarged

The earliest photomicrograph of a piece of wrought
iron. Made by Henry Clifton Sorby in Sheffield in
August 1864. Sorby’s work showed conclusively
that deformation did not destroy crystallinity.

after 1880 to reveal the richness of structure in
metals and alloys, and to associate the changes of
structure with the properties that had been empiri-
cally discovered and long used. Slip bands were
seen in 1896, and in 1900 their nature and
significance were appreciated by Ewing and Rosen-
hain. Slip interference soon became the metallur-
gist’s theory of hardening.

Long before physicists began to get interested in
problems of deformation and the nature of grain
boundaries, metallurgists knew the phenomena in-
timately though empirically, and had developed
their own naive little models to account for the
behavior. Though through most of history the
metallurgist’s closest association has been with
chemists, by the second decade of the twentieth
century they were thinking in physical terms if not
as physicists. Chemists had grown and studied
metal crystals as curiosities lor over a century, but
it was the metallurgist, H. C. H. Carpenter, who
first did significant mechanical tests on single crys-

-

BEFORE OUR TIMES

11

tals of metal, and it was the report of his work
which triggered off G. I. Taylor’s renewed interest
in deformation that culminated in the invention of
the dislocation. Almost a century earlier, collabora-
tion with a practical cutler in work on the alloys
of steel (partly aimed at duplicating oriental Da-
mascus steel) had helped to give Michael Faraday
the sense of structure which so dominated his
thinking.3

I don’t mean to say that metallurgists in the
nineteenth century did not benefit from physics;
indeed, their whole approach was always based
upon a knowledge of college physics, the tamped-
down general level of science which Derek Price
properly regards as being the route through which
science mainly influences technology. Rut it must
be admitted that physicists were usually unable to
work up interest in the complicated problems that
concerned metallurgists. The metallurgist tends
cjuite literally to enjoy the wide range of the be-
havior of metals, while the physicist will look only
at those aspects that are ripe for understanding.

Faraday soon lost interest in metals, and it was
a very good thing for science that he did. A few
other physicists tried to look realistically at solids,
but they had little following. There is the French
physicist, Louis Savart, who in 1829, to explain
the details of Chladni figures on vibrating plates,
made some very acute comments on the structure
of metals. Ffe realized that normally there were
assemblages of a vast number of little crystals
packed together at random, but that preferred
orientation would develop under special conditions
of casting, working, and annealing. He observed
the difference between the static and dynamic
modulus of elasticity, and attributed changes of in-
ternal friction to structural relaxation. The elastic
aftereffect attracted experimentalists, while Boltz-
man and Maxwell provided characteristic theories,
the former purely mathematical, the latter based
on changing molecular aggregations. Others who
were concerned with complicated structures in re-
lation to physical properties were M. L. Franken-
heim and particularly O. Lehmann, whose Mo-
lekular Physik (1889) is a fine museum of phenom-
ena that depend upon crystalline perfection and
imperfection, and he had a sense of form that was
more that of a biologist than a physicist. This
viewpoint, however, did not find its way into text-
books, not even the advanced ones which decided
what things the discipline of physics should be
concerned with.

Finally, no one who, like myself, has experienced
the wonderful stimulation that came to metallurgy
from the impingement of physics in the 1920’s,

and especially right after World War II, can be
blind to results of the joining of two streams of
development that had been to some extent separate.
One cannot deplore the earlier separation, for
neither field was ripe for profitable interaction.
Recently, however solid-state physics has advanced
to the point of becoming a separate profession,
and physical metallurgy has become metal physics.
Though both fields have gained competence and
immense utility, they have perhaps become less
exciting, for the diversity of material behavior has
been reduced to unitary phenomena that are well
understood, at least “in principle.” The framework
for studying complexity is still lacking, and, de-
plorably, the study of it is not encouraged in most
universities.

Metallurgists trained in the 1920’s, as I was,
saw in the richness of visible microstructure a key
to the understanding of most of the phenomena
that their predecessors had discovered and used.
Most developments since then have been on an
atomic scale, especially flowing from the applica-
tion of that marvelous tool, x-ray diffraction. As
a microscopist, however, I have been delighted to
see the recent return to direct observation of the
structures of irregular aggregates of imperfections
with the electron microscope. Great things are
certainly stirring, but I have a little feeling that
with metallurgy and physics now so close together,
the new viewpoint that will trigger off the next
wave of excitement and advance will have to come
from outside. Somehow, I think it must be a con-
cern with far more complex things than have been
allowed in the domain of respectable physics in the
past. I wouldn’t be entirely surprised if it comes
from biology when the high fashion of biology re-
turns from the molecule to the organism. It will
certainly have some of the old natural historian’s
view in it, and it may even have a big dose of
something as unscientific as art, for of all people
the artist seems to be best able to make significant,
if not always precise, statements about very com-
plex interrelationships.

References

1. C. S. Smith, Materials and the Development of Civiliza-
tion and Science, Science, 148, 908 (1965).

2- For an excellent history of corpuscular philosophy, see
Marie Boas, The Establishment of the Mechanical Philos-
ophy, Osiris, 10, 412 (1952). The metallurgical aspects
are mentioned in C. S. Smith, A History of Metallography ,
chapter 8 (University of Chicago Press, Chicago, 1960
and 1965) .

3. L. P. Williams, Faraday and the Alloys of Steel, The
Sorby Centennial Symposium on the History of Metal-
lurgy, C. S. Smith, ed., pp. 145-162 (Gordon and Breach,
New York, 1965).

12

HISTORY OF PHYSICS

Franklin’s physics

“Poor Richard’s” ability to extract the heart from the matter

and express it plainly, evident in his work with electricity, led to the international

scientific reputation that preceded his political missions.

John L. Heilbron

PHYSICS TODAY / JULY 1976

Benjamin Franklin usually receives good
marks for his physics from those who have
taken the trouble to study it. To con-
temporaries he was the “Kepler of Elec-
tricity” (Volta being the Newton), the
“Modern Prometheus,” the “Father of
Electricity.” Among moderns, Robert
Millikan credits him with the discovery of
the electron and brackets him with La-
place as the two greatest scientists of the
18th century. Millikan, whose promotion
of Franklin was perhaps intended to fa-
cilitate a reappraisal of the relative con-
tributions of himself and J. J. Thomson to
the investigation of electrons, went too
far. But one does not have to consider
Franklin a Kepler, Newton, Prometheus
or Millikan to perceive that he was one of
the most important natural philosophers
of the Age of Reason.

Franklin’s international reputation
derived from his work on electricity, done
primarily in the late 1740’s and made
public in the early 1750’s. The reputation
preceded and assisted his political mis-
sions to England and France. (The por-
trait shown in figure 1 was engraved for
sale in Paris.) The relation between his
electricity and his embassy may be taken
as a symbol of the coherence of his life’s
work. The same cast of mind and habits
of thought appear in his science, in his
social and political writings, and indeed
in the conduct of his printing business.

Plus and minus electricity

Franklin took up electricity in the
winter of 1745-6, in his fortieth year,
when his business no longer needed his
full attention and yielded an income that
could support learned leisure. Printing
was by no means an inappropriate prep-

The author is professor of history and director
of the Office for History of Science and Tech-
nology, University of California, Berkeley.

aration for an Enlightenment experi-
mentalist; it taught some of the requisite
qualities, the coordination of head and
hand, familiarity with wood and metal,
exactness, neatness, dispatch. The pro-
ductive English electricians contemporary
to Franklin also came from the higher
trades: William Watson, an apothecary;
John Ellicott, a clockmaker, and Benja-
min Wilson, a painter. And printing, as
practiced by Franklin, brought not only
manual skills but also practice in straight
and accurate thinking. In editing or
composing, the successful printer had to
be clear, economical and pertinent; ev-
erything was set by hand, and paper cost
as much as labor. These experiences
helped to frame Franklin’s style. The
same power of extracting the heart from
the matter and expressing it plainly that
delights us in the sayings of Poor Richard
was ready to serve Franklin when he
began to unscramble the phenomena of
electricity. He also drew upon his expe-
rience of men and institutions. His suc-
cess in building up his business and
shaping his community, in mastering
people and machines, no doubt supported
his characteristic optimism, the expecta-
tion that he could control or cajole his
environment.

The standard electrical demonstrations
of the early 1740’s employed the odd ap-
paratus shown in figure 2. It had been
introduced a decade earlier by Stephen
Gray, formerly a dyer but then a resident
of the London Charterhouse, where
charity boys were always available for use
as capacitors. One caught an urchin,
hung him up with insulating cords, elec-
trified him by contact with rubbed glass,
and drew sparks from his nose. Franklin
witnessed such sport in 1744, when a
travelling lecturer in natural philosophy,
one Dr Spencer of Edinburgh, visited the
middle colonies. It was not Spencer’s

operations, however, that made Franklin
an active electrician, but the gift of a glass
tube to the Library Company of Phila-
delphia (of which Franklin was a founding
member) and the simultaneous appear-
ance in the Gentleman’s Magazine of an
article describing the latest amusements
procurable by electricity.

The Gentleman’s was a lively monthly
of political and intellectual news, pub-
lished in London. The Library Company
subscribed to it, and Franklin probably
read it regularly. He was often the first
to see it, in his capacity as postmaster of
Philadelphia, and he had tried to intro-
duce a colonial version, the General
Magazine for all the British Plantations
in America. This publication had run for
six months in 1741, filled out, as was the
Gentleman’s, with bits and pieces taken
from books and other magazines. The
article on electricity that caught Frank-
lin’s fancy in 1745 was just such a filler, a
translation of a piece published anony-
mously in a literary review called Bib-
liotheque raisonnee. Although written
in French, the review was conducted by
Dutch professors and published in Am-
sterdam (figure 3). The anonymous
contributor of electrical news was Al-
brecht von Haller, the celebrated Swiss
biologist, litterateur and all-round poly-
math, then a professor at the University
of Gottingen. Franklin’s first steps in
electricity were guided not, as has been
thought, by the works of Watson and
Wilson or by his untutored imagination,
but by a popular report in a Dutch journal
of the latest findings of German electri-
cians.

Haller’s account includes a thought-
provoking experiment in which the usual
boy now stands upon insulating supports
of pitch. He grasps or is tied to a chain
electrified by the tube or by a globe spun
by a machine like a cutler’s wheel (figure

BEFORE OUR TIMES

13

4); should anyone approach the boy, a
spark will jump between them, “accom-
panied with a crackling noise, and a sud-
den pain of which both parties are but too
sensible.”

Franklin seized on this experiment,
extended and simplified it, and made it
the basis of a new system of electricity.
Let two persons stand upon wax. Let
one, A, rub the tube, while the second, B,
“draws the electrical fire” by extending
his finger towards it. Both will appear
electrified to C standing on the floor; that
is, C will perceive a spark on approaching
either of them with his knuckle. If A and
B touch during the rubbing, neither will
appear electrified; if they first touch af-
terwards, they will experience a spark
stronger than that exchanged by either
with C, and in the process lose all their
electricity. Gentleman A, says Franklin
in explanation, the one who collects the
fire from himself into the tube, suffers a
deficit in his usual stock of fire, or elec-
trifies minus; B, who draws the fire from
the tube, receives a superabundance, and
electrifies plus; while C, who stands on the
ground, retains his just and proper share.
Any two, brought into contact, will expe-
rience a shock in proportion to their dis-
parity of fire, that democratic element
forever striving to attach itself to each
equally.

The form of this analysis appears to
have been habitual with Franklin. His
first published work, A Dissertation on
Liberty and Necessity, Pleasure and
Pain, which he printed up himself in 1725,
considers the problem of freedom of the
will in much the same terms as he later
used to classify electrical sparks. Since
God is omniscient, omnipotent and all
good, our world, His creation, must be
arranged for the very best: there is no
room for liberty of action. The only cause
for motion in the universe is pain, or

AMERICAN PHILOSOPHICAL SOCIETY LIBRARY

Scientist, philosopher, diplomat. This portrait of Franklin by F. N. Martinet was offered for sale in
Paris with an inscription reading in part . .America has placed him at the head of scholars; Greece
would have numbered him among the Gods." Note the lightning conductor visible through the
window and the electrostatic apparatus behind the chair. Figure 1

14

HISTORY OF PHYSICS

rather its avoidance; fortunately we do not
lack sources of uneasiness, and keep busy
seeking surcease. “The fulfilling or sat-
isfaction of this desire, produces the sen-
sation of pleasure, great or small in exact
proportion to the desire.” Franklin
makes much of the exact proportion, or
rather equality, between the stimulating
pain and the relieving pleasure. The one
supposes the other; should the pain last
until the end, death will bring propor-
tionate relief. Consider A, an animate
creature, and B, a rock. Let A have ten
degrees of pain. Ten degrees of pleasure
must therefore be credited to his account;
“pleasure and pain are in their nature
inseparable.” Let him then have his
pleasure; he thereby returns to the neutral
state, which B has enjoyed throughout.
One cannot miss the analogy between the
animating pain, the inseparable, equal
compensating pleasure, and the inert
rock, on the one hand, and negative elec-
tricity, positive electricity, and the neutral
state, on the other.

The chief result of this analysis, as it
pertained to electricity, was the discovery
of contrary electrical states. The origi-
nality of the discovery is perhaps best
gauged by the extreme reluctance of Eu-
ropeans to accept it. Eventually they did
so, largely on the strength of Franklin’s
analysis of the Leyden jar, which other
contemporary theories could not explain.

The Leyden jar

The Leyden jar charges by accumulat-
ing electrical fire on its internal coating.
The accumulation is made possible by
grounding the external surface; for as
positive electricity develops inside, the
answering negative must be able to es-
tablish itself outside. Franklin believed
that the charging continued until the
outer surface of the bottle was exhausted:
“no more can be thrown into the upper
part when no more can be driven out of
the lower.” He demonstrated the equa-

lity by arranging a cork to play between
wires attached to the coatings, as in figure
5; the cork swings to and fro, carrying fire
from the top to the bottom, until the
original state has been restored.

How does the accumulation produce a
deficit, the plus yield a minus? Franklin
supposes that the bottle’s glass is abso-
lutely impermeable to the electrical
matter; that the particles of electric
matter repel one another; that the repul-
sion operates over distances at least as
great as the thickness of the jar, and that
this macroscopic force, arising from the
accumulation within the bottle, drives out
the electrical matter naturally resident in
the exterior surface of the jar. Most of
these suppositions were peculiar to
Franklin, particularly the odd notion that
the bottle contained no more electricity
when charged than when normal (its
pleasure and pain separate but equal) and
the revolutionary concept of the impen-
etrability of glass. Earlier electricians,
arguing from the exercise of electrical
attraction across glass screens, had con-
cluded that the (material) agent of elec-
tricity could penetrate glass. Since, as
they also knew, glass could insulate
charged bodies (that is, prevent the flow
of electrical matter to ground) they un-
derstood that glass could not transmit
electrical matter very far. But everyone
believed that transmission could occur
over distances of the order of bottle
thicknesses. Electricians were accord-
ingly perplexed to discover, in the case of
the condenser, that a very thin glass,
grounded on one side, could preserve a
very large charge. Several of them es-
caped from their dilemma by the sort of
argument made familiar by the quantum
physicist: Glass is either transparent or
opaque to the electrical matter according
to the experiment tried.

Characteristically Franklin cut through
the paradox by firmly choosing one al-
ternative and ignoring or downgrading the

phenomena that supported the other.
Together with the impenetrability of glass
he perforce admitted action over macro-
scopic distances, a proposition that, de-
spite the success of the gravitational
theory, was still a bugaboo even among
Newtonian physicists. But — and this is
also characteristic — Franklin made no
effort to relate what he took to be the
macroscopic results of the charging to the
primitive repulsive forces that he under-
stood to generate them.

For example, his proposition that the
positive charge on the inner coating
equals the negative on the outer conflicts
with his charging mechanism. The con-
dition for the cessation of charging must
be the vanishing of the force driving
electrical matter into the grounding wire,
and — if the primitive force decreases with
distance, as Franklin supposed it to do —
the macroscopic force can only be an-
nulled when the farther accumulation
exceeds the nearer deficit. The discovery
by later Franklinists of the inequality of
the charges on the two surfaces of the
condenser was to mark a substantial ad-
vance over the theories of the founder.
Of course the advance had been set up by
the acceptance of Franklin’s approach.
He always applauded such improvements
in his theory, it being more important, he
said, that science advance than that he be
considered a great philosopher. He
generously left the second, and sometimes
also the first, approximation to others.

In disregarding the hypothetical dy-
namics of the electrical matter Franklin
distinguished himself from the leading
contemporary European electricians,
from J. A. Nollet in France, Watson and
Wilson in England, and the Germans
mentioned by Haller. Franklin did not
know his colleagues’ habits when he
began; he had not read their papers, and
his cicerone Haller had omitted their in-
tricate theories as imperfect and prema-
ture. He went his way until he met with
the electrical mechanics of Watson and
Wilson. He then devised an alternative
scheme, a specimen of which is illustrated
in figure 6.

In this scheme the positively electrified
spike holds its redundant electrical mat-
ter as a conformal atmosphere. Note that
the portions HABI and KLCB are held by
the large areas AB and BC, respectively,
while HAF, IKB, and LCM rest on much
smaller surfaces. The spike retains its
atmosphere by an attractive force be-
tween electrical and common matter;
hence, Franklin says, it is easy to draw off
electricity from a corner or a point, where
there is little attracting surface. This
scheme, which is not natural to Franklin,
did not earn him high marks for physics.
He unwittingly introduced two inconsis-
tent sets of forces, one to establish the
conformal atmosphere, the other to pre-
serve it; for if the forces that maintained
it determined its shape, it would be shal-
low opposite points and deep opposite

Stephen Gray's charity boy. Suspended by insulating cords and charged with a rubbed glass rod,
the boy could provide diversion tor onlookers by having sparks drawn from his nose or (as in the
illustration above) by attracting bits of leaf brass. (From J. C. Doppelmayr, Neu-entdeckte Phae-
nomena, Nuremburg, 1744.) Figure 2

BEFORE OUR TIMES

15

Blbliotheque ralsonee. The title page of the first volume (1728) shows
one of its enlightened reviewers at work. Franklin’s attention was drawn
to electrical experiments by an article, originating in this review, translated
for Gentleman's Magazine. Figure 3

Another human capacitator, this time erect; he again attracts leaf brass,
as at A and B. His flying hair and the fluff on his shoulder demonstrate
the repulsive force of electricity. (From J. A. Nollet, Essai sur I’electricite
des corps, Paris 1746). Figure 4

plains. Again, the primitive forces pro-
posed— attraction between the elements
of common and those of electrical matter,
repulsion between particles of the elec-
trical— conflict with the fact that neutral
bodies do not interact electrically. Let
the quantities of electrical and common
matters in the first body be E and M,
those in the second e and m. Then £ will
be attracted by m and repelled by e, but
M will be drawn by e without compen-
sating repulsion. Similarly there is an
unbalanced attraction on m. Franklin’s
electrical mechanics, the result of an at-
tempt to copy continental physicists, re-
quire unelectrified bodies to run together.

Lightning

The same indifference to the exigencies
of the forces he introduced appears in
F ranklin’s theory of the lightning rod. So
does the same bold process of simplifica-
tion that discovered the contrary electri-
cities and insisted upon the electrical
opacity of glass. That lightning and
electricity agreed in many properties was
a commonplace when Franklin took up
the subject; Haller, for example, empha-
sized the parallel between the transmis-

sion of electricity along an insulated string
and the direct path of lightning along the
“wire of a steeple clock from top to bot-
tom” (so the Gentleman's mistranslates
“un fil d’archal qui servoit a faire sonner
une clochette sur le haut d’une tour”).
In 1748 the Bordeaux Academy of Sci-
ences offered a prize for an essay on the
relation between lightning and electricity.
It was won by a physician who took as his
byword an old conceit of Nollet’s:
“I’electricite est entre nos mains ce que
le tonnerre est entre les mains de la na-
ture.”

One of Franklin’s collaborators dis-
covered that a grounded metallic point
could quietly discharge an insulated iron
shot at some distance, while a blunt object
could extract the electricity only when
very near, and then suddenly, noisily, and
with a show of sparks. Whence the dif-
ference? According to Franklin’s
homemade physics, the point acts only
upon the small surface of the shot directly
facing it; it therefore can pull away the
redundant electrical matter a little at a
time, as the excess redistributes itself to
compensate for the loss of the portion just
removed. “And, as in plucking the hairs

from a horse’s tail, a degree of strength
not sufficient to pull away a handful at
once, could yet easily strip it hair by hair;
so a blunt body presented can not draw
off a number of particles [of the electrical
matter ] at once, but a pointed one, with
no greater force, takes them away easily,
particle by particle.”

Franklin’s bold and optimistic imagi-
nation immediately assimilated the shot
to a thunder cloud and the pointed punch
or bodkin to an instrument capable of
robbing the heavens of their menacing
electricity. To illustrate and confirm his
thought, he invented a straightforward
but misleading laboratory demonstration,
easily reproduced. Take a pair of brass
scales hanging by silk threads from a
two-foot beam; suspend the whole from
the ceiling by a twisted cord attached to
the centeT of the beam, maintaining the
pans about a foot above the floor; set a
small blunt instrument like a leather
punch upright on the ground. Now el-
ectrify one pan and let the cord unwind;
the charged pan inclines slightly each
time it passes over the punch until the
relaxation of the cord brings it close
enough for a spark to jump between them.

16

HISTORY OF PHYSICS

Experiment and observation. Franklin’s most persuasive demonstration (figure 5) of the qualitative
difference between the electrifications of the two coatings of a Leyden jar: the cork f oscillates
between the points e, fetching the surplus electricity from the interior of the bottle to make up the
deficit of the outside coating d. His analysis (figure 6) of the binding of electrical atmospheres
postulates an attractive force between electrical and common matter, and the sentry box (figure
7) illustrates his design for bringing down lightning from the clouds. (From Franklin, Experiments
and Observations on Electricity, London, 1751—54.) Figures 5,6,7

If, however, you mount a pin, point up-
permost, atop the punch, the pan silently
loses fire to the point at each pass and, no
matter how close it approaches, never
throws a spark into the punch.

It was no doubt his faith in the power of
points that allowed Franklin to go beyond
the European electricians who had con-
tented themselves with suggesting an-
alogies between lightning and electricity.
Why not catch a little lightning and make
it do the usual electrical parlor tricks?
The probe would have to be insulated, but
Franklin apprehended no danger, prob-
ably because he believed that a sharply
pointed rod would bring down lightning
slowly enough to allow the observer to
prevent dangerous accumulations. He
accordingly proposed, in 1750, that a
sentry box containing an insulating stand
A (figure 7) be mounted on a tower or
steeple; an iron rod, projecting 20 or 30
feet above the box, would fetch the light-
ning, which the sentry would draw off in
sparks. The sight, sound, smell and
touch of the sparks would confirm the
identity of lightning and laboratory elec-
tricity.

Franklin did not try this dangerous
experiment himself; much of Poor Rich-
ard’s caution was native to his inventor.
The drama was first staged in France, in
1752, by a clique headed by G. L. Leclerc,
later comte de Buffon, who had found the
electrical theories of the unknown printer
from Philadelphia useful ammunition in
his bitter feud with R. A. F. de Reaumur,
who supported the traditional approach
to electricity of his protege Nollet. Buf-
fon’s agents, sharing Franklin’s caution,
did not expose themselves to thunderbolts
either. They engaged a retired dragoon
to draw the sparks; fortunately for the old
soldier the rod picked up only minor
electrical disturbances in the lower at-
mosphere. The first to perform Frank-
lin’s experiment as initially conceived was
a member of the Petersburg Academy of
Sciences, G. W. Richmann. The thun-
derbolt that he enticed into his home
killed him instantly.

Richmann had known that he ran a
risk. “In these times [he said] even the
physicist has an opportunity to display his
fortitude.” There was good evidence that
Franklin’s sentry might be in peril. As
Haller had observed, lightning liked to
run down wires and ropes attached to
church steeples. Often enough the other
ends of these ropes were held by men en-
gaged in the standard early-modern de-
fense against lightning — ringing bells.
Now the destruction of bellringers by
lightning had been remarked, and
Franklin’s sentry stood in the same rela-
tion to his box and rod as the bellringer
did to his church and steeple. In fact
Franklin tacitly admitted the danger of
his sentry in his consequential proposal to
replace bellringers by grounded rods as
protection against lightning. (The
practice of breaking up thunder clouds by

sounding bells was outlawed in several
places in the 1770’s and 1780’s; not so
much on physical or humanitarian prin-
ciples, it must be confessed, but for noise
abatement.)

That Franklin did not conclude, from
the protective role of the grounded rods,
that insulated ones might be very dan-
gerous agreed with his usual sanguinity.
His confidence rested, as already sug-
gested, on his belief in the analogy of na-
ture, on his extrapolation from the silent
discharges effected by points in the lab-
oratory to the operations of iron rods on
thunder clouds. The same sort of ex-
trapolation may perhaps be seen in his
optimistic political and social philosophy;
he appears to have considered organiza-
tion at the federal level to be analogous to
local combinations, without regard to
scale.

The Franklinist faith in the power of
points may be illustrated by the mock-
heroic battle of the knobs and spikes,
which broke out in the late 1770’s when a
British power magazine, defended by
sharp grounded rods as directed by
Franklin, suffered minor damage from
lightning. Wilson immediately located
the trouble in the points. In elaborate
experiments conducted in a London
dance hall grandly named “The Pan-
theon” (figure 8) he showed, what no one
doubted, that, pointed conductors dis-
charged electrified bodies at greater dis-
tances than blunt ones. Since, he said,
Franklin’s points evidently do not draw

down lightning silently, but are struck just
like blunt rods, it is only prudent to ter-
minate lightning conductors obtusely; for
loaded clouds that would strike to pointed
rods might, if high enough, pass harm-
lessly over blunted ones.

Wilson’s large-scale experiments had
been made possible by George III, to
whom he had access through aristocrats
whose portraits he had painted. Franklin
had represented the disobedient colonies
which, at the time of the Pantheon dem-
onstrations, were in full revolution. The
shape of lightning conductors became a
matter of politics. The King (according
to a fine story perhaps invented by the
French) instructed the President of the
Royal Society, Sir John Pringle, that
lightning rods would henceforth end in
knobs. Pringle, a great friend of Frank-
lin’s, replied that the “prerogatives of the
president of the Royal Society do not ex-
tend to altering the laws of nature,” and,
according to the story, forthwith resigned.

Fortunately neither the cause of the
Revolution nor the efficacy of lightning
rods rested upon the suppositious ad-
vantage of points over knobs. The anal-
ogy that Franklin trusted does not hold:
on Nature’s scale, on the scale of thun-
derclouds, points and knobs appear about
the same; “obtuse Wilson” (as the Fran-
klinists called him) was quite right in in-
sisting that pointed rods cannot quietly
despoil clouds of lightning. And yet, even
though the analogy does not hold, the
optimism expressed by it, the expectation

BEFORE OUR TIMES

17

that experience with puny effects of our
own creation- can guide us to the control
of the great powers of Nature, was not
misplaced. Lightning rods work. The
aristocratic hanger-on, Wilson, warned
that we must not expect “anything like
absolute security” in such matters. The
optimistic republican, Franklin, trusted
that Nature could be mastered.

Utility

Several passages in Franklin’s writings
suggest that he cultivated science chiefly
with an eye to its utility. In a report of
electrical experiments dated 1748 he de-
clared himself “chagrined a little” that his
work on electricity had not yet produced
anything “of use to mankind.” The best
he could offer were imaginary improve-
ments on electrical games described by
Haller — a picnic on an electrocuted tur-
key, roasted on an electrical jack before a
fire ignited by an electric spark; a toast to
the electricians of Europe, drunk from
electrified bumpers (small, thin, nearly-
full wine glasses charged as a Leyden jar)
“under the discharge of guns from the
electrical battery.” This playfulness dis-
appeared from Franklin’s account of ex-
periments undertaken to show that
light-colored cloths “imbibe” the heat of
the Sun less readily than dark ones.
“What signifies philosophy [he then said]
that does not apply to some use?” He
goes on to recommend white clothes for
the tropics. In another place he writes as
if the practical implications of natural
laws are for him the main objective. “It
is of real use to know that china left in the
air unsupported will fall and break; but
how it comes to fall, and why it breaks, are
matters of speculation. It is indeed a
pleasure to know them, but we can pre-
serve our china without it.” To this evi-
dence may be added the testimony of his
inventions, the Pennsylvania fireplace,
bifocals, the glass harmonica and, above
all, the lightning rod.

Yet, for all his emphasis on utility,
Franklin cultivated science primarily for
intellectual pleasure. The message about
china plates follows immediately upon the
highly conjectural analogy between the
power of points and the stripping of a
horse’s tail. Franklin constantly built up,
and as often discarded such “pretty sys-
tems”; the principal use of which, he said,
was the discarding, for that might “help
to make a vain man humble.” He spoke
of his work in electricity not as a hopeful
inventor, but as an eager savant. “I never
before was engaged in any study that so
totally engrossed my attention and my
time as this has lately done,” he wrote in
1747. “What with making experiments
when I can be alone, and repeating them
to my friends and acquaintances, who,
from the novelty of the thing, come con-
tinually in crowds to see them, I have,
during some months past, had little lei-
sure for anything else.” Franklin may
have hoped that something practical

The Pantheon experiment. A model of the powder magazine (shown at the right), armed with
grounded points or knobs, was drawn on rails under the huge cylinders electrified by the machine
in the center background. The cylinders represented clouds, the motion of the model their drift
over the magazine. (From Benjamin Wilson's paper in Philosophical Transactions of the Royal
Society of London, 68:1, 239-313, 1778.) Figure 8

would emerge from his studies, but he did
not study primarily for utility. In the
case of electricity he set the principles of
the subject and developed them in ana-
lyzing the condenser before he sought
practical applications.

Perhaps Franklin’s most frivolous
study was magic squares. He indulged
his taste for these useless toys for several
years, until he acquired such a “knack . . .
that I could fill the cells of any magic
square, of reasonable size, with a series of
numbers as fast as I could write them,
disposed in such a manner as that the
sums of every row, horizontal, perpen-
dicular, or diagonal, should be equal.”
But this by no means satisfied him; he
invented supererogatory tasks, the cre-
ation of grids with bizarre additional
symmetries, such as the great 16 X 16
table published in the Gentleman’s
Magazine in 1768. It was, as Franklin
allowed in terms far from utilitarian, “the
most magically magical of any magic
square ever made by any magician.”

Poor Richard nonetheless felt obliged
to apologize for time wasted on number
magic. He took up the squares, he said.

to pass the time (“which I still think I
might have employed more usefully”)
when, as clerk of the Pennsylvania As-
sembly, he was obliged to sit through
much tedious government business.
Filling in squares therefore did have some
utility: it kept Franklin awake, and made
him appear alert, at meetings he would
have preferred to miss. For our era, the
Age of the Committee, Franklin’s appli-
cation of the ancient magic square as an
antidote to boredom could be a most
useful invention. □

For further reading . . .

Most of the quotations from Franklin come
from his Experiments and Observations on
Electricity, the data about the history of
electricity are taken from John Heilbron's
Electricity in the 17th and 18th Centuries: A
study of early modem physics, Berkeley
(1979). Additional pertinent information
may be found in I. B. Cohen, Franklin and
Newton, Philadelphia (1956) and in Carl
van Doren, Benjamin Franklin, New York
(1938).

18

HISTORY OF PHYSICS

A Sketch
for a History

of EARLY

THERMODYNAMICS

By E. Mendoza PHYSICS TODAY / FEBRUARY 1961

ACCOUNTS of the origins of the first and second
laws of thermodynamics follow a fairly stand-
ard pattern. The caloric theory of heat, we are
told, assumed that heat was a fluid endowed with a
number of properties, among them indestructibility.
The cannon-boring experiments of Rumford (1798)
and the ice-rubbing experiment of Davy (1799) de-
stroyed the basis of the caloric theory because they
showed that heat could be created by the expenditure
of work. A full half-century elapsed, however, before
Joule repeated and extended Rumford’s experiments
and measured the conversion factor J accurately with
his paddle wheels. In the meantime (in 1824) Carnot
formulated the second law of thermodynamics and drew
many valid conclusions about the efficiency of heat en-
gines though his ideas were based on the caloric theory.
Kelvin came across Carnot’s work, as rewritten by
Clapeyron; he became convinced of its truth and be-
cause it was based on the caloric theory he found it
difficult to accept Joule’s results. However, by 1850
both Kelvin and Clausius had formulated the first and
second laws as we know them now. In retrospect, the
caloric theory of heat seemed to have been slightly
ridiculous.

It seems to me that the pattern just sketched out is
incorrect in many ways. It is particularly unfortunate
that it should be so, for the discovery of the first law
is an episode in the history of physics which can be
studied by students as an example of the way that the
great ideas of science have evolved.

The facts seem to be that the caloric theory did not
reach its highest state of development till after the
work of Rumford and Davy had (in our modern view)
destroyed its very basis — indeed these same experiments
were regarded by the physicists of the time as enrich-

E. Mendoza is senior lecturer in physics at the Physical Laboratories
of Manchester University in England.

ing the caloric theory, as filling in some of the missing
details. Further, at its highest point, the caloric theory
was sophisticatedly mathematical; the properties of the
caloric fluid — the model behind the abstract mathe-
matics— were rarely stressed and were indeed usually
regarded as irrelevant. The mathematics predicted most
of the correct results, and where the equations differed
in essential ways from our own correct ones, there were
reputable experimental results to support them. Finally,
when the modern two laws of thermodynamics were
formulated, the whole of the mathematical apparatus
of the caloric theory was taken over. The attitudes of
modern thermodynamics, with its jargon of perfect dif-
ferentials and of partial differential coefficients, were
inherited from the previous epoch. Perhaps this account
implies that science does not progress tidily, but I think
it is worthwhile giving.

The Two Theories of Heat

THE two hypotheses — that heat was a mode of mo-
tion of the particles of bodies, and that heat was a
substance — had their origins in two quite different sets
of observations. The obvious production of heat by
friction gave rise to the one; indeed the mechanical
theory of heat is by far the more ancient of the two.
On the other hand, the idea of the conservation of
heat in calorimetric experiments was only conceived in
the eighteenth century. Joseph Black had defined sev-
eral interlocking quantities — temperature, specific heat,
latent heat, and quantity of heat — and had at the same
time postulated the conservation in a thermal mixing
process. Then with the rise of the atomic theory and
the discovery of oxygen, many quantitative things could
be explained by the idea that heat was a gas of inde-
structible atoms. The conservation of heat was assured
on this model; further, the atoms of caloric could enter
into chemical combination with the atoms of a sub-

BEFORE OUR TIMES

19

stance (when the heat was latent) or be free (when the
heat could affect a thermometer). In Lavoisier’s view,
the caloric atoms were an essential constituent of oxy-
gen and their release gave rise to the heat of com-
bustion. Thus, in contrast to the old-fashioned dynami-
cal theory, the caloric theory of heat used a few basic
ideas of the up-to-date atomic theory and could explain
beautifully the facts of combustion and calorimetry.

Yet the French physicists and chemists always kept
it firmly in mind that there were two hypotheses which
at the time were equally valid. Every statement of the
theory of heat invariably placed the two theories side
by side, usually with a statement that the two, though
seemingly quite different, must be only varied aspects
of the same underlying cause. There was no obvious
contradiction between the two hypotheses. One of the
earliest statements of this kind comes from the Memoir
on Heat written by Laplace and Lavoisier in 1786.
They state:

We will not decide at all between the two foregoing
hypotheses. Several phenomena seem favourable to the
one, such as the heat produced by the friction of two
solid bodies, for example; but there are others which
are explained more simply by the other — perhaps they
both hold at the same time. ... In general, one can
change the first hypothesis into the second by chang-
ing the words “free heat, combined heat and heat re-
leased” into “vis viva, loss of vis viva and increase of
vis viva".

Here we may note that the words “heat” and “caloric”
w'ere always regarded as interchangeable and that the
vis viva — the living force — of a system of particles was
twice the kinetic energy. The identity of the two theo-
ries is therefore explicitly stated. This statement,
though an early one, is typical of all those written by
French scientists for the next sixty years.

This means that the French scientists did not con-
sider that the issue was straightforward — that either
the caloric theory was true or the dynamic theory; on
the contrary, they held that both were true. Thus it was
that Rumford’s work had very little impact on them.
For example, one of his papers described how he meas-
ured the density of caloric by weighing some ice and
then reweighing it after it had melted, concluding that
the density of caloric, if it existed at all, was negligible.
Subsequent accounts of the caloric theory therefore in-
corporated the additional statement that the mass of
the caloric atoms was very small — like electricity. Fur-
ther, in his other experiments, Rumford showed that
the supply of heat produced by friction was apparently
inexhaustible. Subsequent statements of the caloric the-
ory therefore included the additional statement that the
number of caloric atoms which could be rubbed off by
friction was negligible compared with the number actu-
ally inside a body — like frictional electricity.

It is usually said that the first symptom of the in-
adequacy of any theory is observed when each new
experiment demands that a new hypothesis be added.
From our modern viewpoint these additions to the
caloric theory were of just this kind. But from the con-

Pierre Simon Laplace, who dominated the French
Academy of Sciences in his later years.

( Culver Pictures, Inc.)

temporary point of view they were extremely reason-
able statements. Far from killing the caloric theory.
Rumford’s experiments added to the understanding of it.

The British scientists, in contrast to the French, were
mostly interested in chemistry and atomic theory and
therefore adopted the caloric view uncritically. Rarely
were the two theories placed side by side for fair com-
parison in their writings. Even Davy used caloric con-
cepts when he found them convenient. But it was in
France that the most significant developments were
made, in the decade from 1810 to 1820.

Perfect Differentials

* I AHE mathematical version of the caloric theory
gradually evolved in a series of papers by Laplace
and Poisson. By 1818, the theory of heat was usually
cast in the following form — the quotation is from a
brief introductory paragraph in a paper by Poisson:

Let p be the density of a gas, d its centigrade tempera-
ture, p the pressure which it exerts on unit area, the
measure of its elasticity: then one has

p = ap ( 1 + a.6)

where a and a are two coefficients. . . . The total
quantity of heat contained in a given weight of this
gas, in a gram for example, cannot be calculated: but
one can consider the excess of this Quantity over that

20

HISTORY OF PHYSICS

contained in a gram of gas at an arbitrarily chosen
pressure and temperature. Designating this excess by q,
it will be a function of p, p and 6, or simply of p and
P since these three variables are connected by the pre-
ceding equation; thus we have

7 =

where / indicates a function whose form must be found.

By defining q as the excess quantity of heat over an
arbitrary zero, Poisson avoided the difficulty that the
absolute quantity of heat was much greater than what
could be rubbed off by friction. By stating that q was
a unique function of the thermodynamic coordinates —
for this is the significance of the second equation — he
summarized tersely many experimental facts, for exam-
ple the equality of the latent heats of boiling and con-
densation, or what we should now call the uniqueness
of the enthalpy as a function of pressure and tempera-
ture.

We may put this analytical statement into perspec-
tive by stating for comparison the starting points of
elementary modern thermodynamics. In such treat-
ments, we first restrict ourselves to systems which have
single-valued equations of state, and then we postulate
that there are two independent heat-like quantities
which are single-valued functions of the thermodynamic
coordinates — we usually choose the internal energy U
and the entropy S, which can be expressed as U(p,V)
and S(p,V). In short, the caloric theory differed from
our own approach in that it recognized only one law of
thermodynamics — one heat function q(p,V) — where we
have twTo.

Laplace and Poisson then used this analytical law to
calculate the temperature rise of a gas when it was
compressed adiabatically, to explain the experimental
results of Clement and Desormes. Since q was a unique
function of p and V, dq could be expressed (in modern
notation) as

dq = (dq/dp)vdp + (dq/dv)pdv

— ( 8q/dT)v(dT/dp)rdp + (dq/dT)p(dT/Bv)pdv
— Cv-V ■ dp/R + Cp-p-dV/R (1)

putting the specific heats as dq/dT with suitable sub-
scripts, and substituting pV = RT. Assuming that the
specific heats were constant with temperature the equa-
tion was then integrated to give

Q = f(pVv). (2)

In an abiadatic change the total quantity of heat did
not alter; hence such a change was governed by the law

pVv = constant.

It is well known that Laplace corrected Newton’s ex-
pression for the velocity of sound, assuming that the
wave motion was adiabatic instead of isothermal; this
was his method of calculation. Thus the assumption
that the quantity of caloric was a unique function of
the pressure and volume of a gas allowed the velocity
of sound to be correlated with direct measurements of
the ratio y. It was something of a triumph and was ob-

Delaroche & Berard’s apparatus. Gas con-
tained in B and B' was driven through ap-
paratus by heads of water in vessels A and
.4' in the room above. Normally it ex-
changed heat in the little spiral in the
other half of diagram ; the apparatus is,
however, shown arranged for finding the
heat capacity of the spiral by forcing hot
water through it.

viously proof of the correctness of that basic assump-
tion.

It took later scientists many years to realize that this
same result, that the ratio of adiabatic and isothermal
elasticities of a gas is equal to the ratio of two suitably
defined specific heats, follows straight from the defini-
tions, and results from any physical model of heat
whatever.

Pistons and Cycles

f ■ 'HE mathematical approach to thermodynamics is
essentially the same as that which we use today.
The other approach, using cycles of operations with
frictionless pistons, was evolved by Sadi Carnot. He
was capable of an extraordinary precision of thought
and was no mean mathematician. But his single pub-
lished work, Reflections on the Motive Power of Fire
(1824), was conceived as a popular book for engineers,
to stimulate them into designing better heat engines.
Thus all his proofs and theorems are based on the ac-
tions of engines, however idealized. His concept of the
cycle of operations was consciously based on the as-
sumption of the uniqueness of the quantity of heat as
a function of coordinates; he had probably been taught
that theorem at his Army Engineering School, the Ecole
Polytechnique, where Laplace and Poisson were in-
structors.

In perspective, we can see that this pictorial ap-
proach had a comparatively short life. After Clausius
used it in 1865 to derive the concept of entropy and
thereby show that the two laws of thermodynamics
could be expressed in the same way as the old caloric
theory, the more mathematical approach became domi-
nant once more; pistons and cycles were relegated to
teaching textbooks.

Experimental Proofs

THE rise of temperature of a gas when it was com-
pressed suddenly would be easily explained on the
model that caloric itself was atomic — the heat atoms
were squeezed out from the gas atoms “like water from
a sponge”. This qualitative idea was however given
quantitative expression; it followed from equation (2)
above.

Laplace made the assumption that the function / was
the simplest possible — that it was linear. Thus the heat
content of a gas could be written

q -A + B- T-p^-yVy

where A and B were constants, p and T being chosen

BEFORE OUR TIMES

21

here as the appropriate variables. The specific heat Cp
followed by differentiating with respect to T, showing
at once that it was proportional to the pressure raised
to the- power (1 — y)/y. Putting y= 1.4, the specific
heat of air should decrease approximately as the cube
root of the pressure.

Carnot on the other hand deduced a number of theo-
rems leading to a slightly different result — his method
gave the form of the function explicitly and showed
that the heat content and the specific heat decreased
with the logarithm of the pressure. But both Carnot’s
and Laplace’s expressions, though different in detail,
predicted decreases of specific heat with pressure, show-
ing that a rise of pressure should release heat and so
cause a rise of temperature. They were the quantitative
expressions of the “squeezing out” process.

The experimental measurements of Delaroche and
Berard of the specific heats at atmospheric pressure of
a large number of gases were performed in 1812 and
deservedly won a prize award by the Institut de France.
Their apparatus was beautifully designed, their tech-
niques were highly developed, and most of their results
were accurate. Unfortunately they also performed two
measurements of the specific heat of air at one value
of the pressure slightly above atmospheric — to be pre-
cise, at 1006 mm pressure. They found that for this
30% increase the specific heat of unit mass of air was
reduced by about 10%, which agreed almost exactly
with Laplace’s prediction. This observation remained
for years one of the cornerstones of the whole caloric
theory.

Carnot later compared the same observations with

22

HISTORY OF PHYSICS

his own expression and concluded that the coefficient
of the log p term was small. In 1837, von Suerman in
Germany performed measurements on air at reduced
pressures, finding that Carnot’s formula (or more pre-
cisely Clapeyron’s version of the same expression)
fitted better and that Laplace’s assumption was not
correct. But everyone was agreed that there was a
variation of specific heat, in conformity with the pre-
dictions of the caloric theory.

Thus by the late 1830’s a considerable body of ex-
perimental results had been accumulated and an ad-
vanced mathematical technique had been evolved in
support of the caloric theory. At the same time, these
decades were alive with speculation about the dynami-
cal theory of heat. Claims have been advanced on be-
half of several people as the real originators of the
First Law — but few of these ever wrote down an equa-
tion or quoted numbers other than isolated estimates
of / which proved nothing. Even Mayer's brilliant in-
tuitions were largely concerned with qualitative specu-
lations about the conservation of energy in different
forms; there was little that was quantitative and even
that could be explained on existing theories. In Pois-
son’s phrase, the undulatory theory of heat was sterile.

Carnot and the First Law

THE dynamical theory implied that the heat con-
tent q was not a unique function of pressure and
temperature and that the single law of thermodynamics
was wrong. But this essential point was still not recog-
nized by all physicists. Perhaps they took refuge in the

A sketch taken from Carnot’s private manu-
script notes (the original is one inch high),
showing a proposed experiment on free ex-
pansion of gases. It was not until 25 years
had elapsed that Joule and Thomson pro-
posed and performed this experiment.

postulate that the quantities of heat so evolved were
small compared with the total so that the error of the
assumption was small; perhaps they did not believe
that the supply of heat produced by friction was really
inexhaustible. At any rate, it is astonishing to find a
person as critical as Clapeyron writing (in 1834) only
two or three pages before explicitly stating the unique-
ness of the heat function:

It follows that a quantity of mechanical action and a
quantity of heat which can pass from a hot body to a
cold body are quantities- of the same nature, and that
it is possible to replace the one by the other; in the
same manner as in mechanics a body which is able to
fall from a certain height and a mass moving with a
certain velocity are quantities of the same order, which
can be transformed one into the other by physical
means.

Clapeyron was discussing the functioning of heat en-
gines, not the nature of heat, when he wrote this para-
graph, but the implication was nevertheless quite clear.
The opinion of Laplace and Lavoisier, that there was
no conflict between the two theories of heat, was still
held.

Possibly the only person who grasped the essential
conflict was Carnot himself. In fact he occupies a spe-
cial position in any history of the subject because,
though he only published the one short book on heat
engines, some notebooks of his have been preserved in
which he mused about the shortcomings and improb-
abilities of the caloric model, and gradually groped to-
ward the equivalence of heat and work. These notes
constitute a revealing record of the objections which
could at that time be raised against the dynamical the-
ory. Mostly they stem from the fact that there was no
clear picture of the structure of atoms or of solids, so
that the nature of the thermal agitation of atoms in
solids could not be imagined. For example, Carnot
states that if heat is what we now call energy then the
fact that the whole universe cannot be imagined to run
down must imply (on the dynamical theory) that atoms
cannot touch one another; for if they did touch there
would be friction and the heat vibrations would die
down. In that case he was unable to visualize what
forces could hold the atoms in position in a solid if
they were not touching. Any forces would have to act
through an ether; since an ether had to be a fluid, it
too had to be atomic in structure, so the difficulty could
not be solved. Finally, however, he explicitly stated the
equivalence of heat and work, leaving the question of
the microscopic picture unsolved. He estimated J quite
accurately.

A careful examination of these notebooks together
with the manuscript of Carnot’s book on heat engines
and the published version of it shows that he had
started on this train of speculation about the First Law
at the same time as he was writing about the Second.
Certainly by the time he came to correct the proofs of
his book he had realized that the very basis of all his
theorems and demonstrations was wrong. For example.

BEFORE OUR TIMES

23

James Prescott Joule as he appeared
at the time of his classic experiments.

concerning his theorem that the motive power of heat
is independent of the working substance, he originally
wrote :

The fundamental law which we proposed to confirm
seems to us to have been placed beyond doubt. . . .
We will now apply the theoretical ideas expressed
above to the examination of the different methods pro-
posed up to now for the realisation of the motive
power of heat.

But in the printed version he altered this to:

The fundamental law which we proposed to confirm
seems to us however to require new verifications in
order to be placed beyond doubt. It is based on the
theory of heat as it is understood today, and it should
be said that this foundation does not appear to be of
unquestionable solidity. New experiments alone can de-
cide the question. Meanwhile we can apply the theo-
retical ideas expressed above, regarding them as exact,
to the examination of the different methods proposed
up to now for the realisation of the motive power of
heat.

He had realized that the Law q = f(p,V) was no longer
true and this destroyed the idea of the cycle of opera-
tions. He had discovered the First Law to the exclusion
of the Second. The essential step of postulating that
there were two independent laws was too difficult to
take.

The point of this episode is that we know that Sadi
Carnot was a reserved and taciturn man, something of
a perfectionist. It is therefore extraordinary that he
allowed the publication of his book to proceed after he

had begun to doubt his own methods. We can only be
thankful that this is what he did.

(It is unfortunate that something of a “mystique” has
grown up around Carnot's writings. From his use of the
word “caloric” it has been deduced that he had a pre-
vision of the concept of entropy. However, the words
he used were merely interpretations of the equations he
wrote down, and it is clear that together with those
written down by all other contemporary physicists,
these equations were only true by coincidence.)

Joule's Experiments

JOULE'S first research (started when he was aged
19) was on the design of electric motors. Though
these early machines were spidery little affairs hardly
recognizable as the forerunners of those familiar to us,
Joule envisaged them as the prime movers of the fu-
ture. At first he thought of them as possible perpetual
motion machines, but the i2R formula for the heating
effect of a current was an early result of the investiga-
tions. He also found that the attractive force of an
electromagnet was proportional to z2, and the simi-
larity of the formulas led him to think of a connec-
tion between mechanical and heating effects. Eventually
he was led to do a remarkable experiment with a sim-
ple dynamo whose armature was immersed in a rotat-
ing vessel full of water. With the armature stationary
and connected to a battery he measured the heating;
by rotating the armature he superimposed a second cur-
rent and found that he could create or destroy heat ac-
cording to the sense of rotation. The change of heating
was proportional to the work done in rotating the arma-
ture. This experiment, in Joule’s view, showed conclu-
sively that the accepted theory of heat was wrong and
he started at once on a series of experiments of great
variety to prove his point of view.

The electrical experiments had given / = 4.60 joules/
calorie in our modern units. The heating of water forced
through narrow holes in a piston gave 4.25 units; heat-
ing by the friction of two solid surfaces rubbing be-
neath water or mercury gave the same value. He
pumped air into a cylinder to 22 atmospheres and
measured the heat produced in the cylinder; comparing
this with the pV term, J emerged as 4.60 units. Then
he allowed the gas to escape slowly — the cylinder cooled
and J was found to be 4.38 units. But when the gas
escaped slowly from the high-pressure cylinder into an-
other, without performing external work, the cooling of
one cylinder was equal to the heating of the other so
that there was no net production of heat. These experi-
ments took him five years to do — from 1843 to 1848.

After these experiments were finished Joule allowed
himself to speculate on the philosophical and other as-
pects of the theory. It was, however, the quantitative
aspect of his work which eventually carried conviction.
The conversion factor was the same within 15% how-
ever the work was performed: electromagnetically, by
solid or liquid friction, or by the changes of volume of
a gas. This could not be plausibly explained on any

24

HISTORY OF PHYSICS

caloric model. Two years after this series of experi-
ments he measured J accurately by stirring water with
paddle wheels, but these experiments were relatively
unimportant.

Joule wrote a number of papers about his work but
till almost the end of this important epoch he was in-
tellectually quite isolated. The commonest objection to
his theory was that it all depended on temperature
rises of a few hundredths of a degree, which could
hardly be significant enough. But two papers, Grove’s
“On the Correlation of Physical Forces” and Helm-
holtz’ “On the Conservation of Force” helped to pre-
pare the intellectual climate for the acceptance of
Joule’s theory.

Clapeyron’s paper on the motive power of heat had
been published in England in 1837, in Taylor’s Scien-
tific Memoirs, a journal which specialized in transla-
tions of foreign papers; Joule was familiar with it.
By 1844 he w'as already confident enough to reject
Clapeyron’s description of the cycle of operations in
the steam engine. He flatly contradicted the view that
the passage of heat from boiler to condenser was suffi-
cient to produce work. For the first time, the issue ap-
peared to be clear — either Carnot or Joule was right.

Synthesis

ViyiLLIAM THOMSON (Lord Kelvin) seems to
' ’ have been the key figure in the synthesis of the
tw'o theories. He w'orked in Paris as a sort of research
assistant in Regnault’s laboratory in 1845 and there
learned of Clapeyron’s paper. He proposed the work
scale of temperature wholly in caloric terms. Though
he became a close friend of Joule, had a deep respect
for his experiments, and always quoted his opinion, he
could not accept the newer theory. His principal objec-
tion was that there were no examples of the reverse
conversion of heat into work. Joule wrote to him that
the Peltier effect could provide one such process, but
it took Thomson four years to understand this remark.
In 1849, Thomson published an account of Carnot’s
theory. There were many references to Joule’s work
but the “ordinarily received and almost universally ac-
knowledged” principle that heat was conserved in a
cycle of operations w'as still the accepted basis. Later
in the year William’s brother James published theoreti-
cal predictions based on Clapeyron’s equation for the
lowering of the freezing point of water by pressure;
experiments confirmed the predictions — and hardened
Thomson’s conviction that Carnot’s methods and the
theory it was founded on were true.

The change of viewpoint happened quite suddenly.
Probably Clausius was the first to see that there were
two independent principles. In 1850 he wrote:

It is not at all necessary to discard Carnot’s theory en-
tirely, a step which we certainly would find it hard to
take since it has to some extent been conspicuously
verified by experiment. A careful examination shows
that the new method does not contradict the essential
principle of Carnot, but only the subsidiary statement
that no heat is lost, since in the production of work it

may well be that at the same time a certain quantity
of heat is consumed and another quantity transferred
from a hotter to a colder body, and both quantities of
heat stand in a definite relation to the work that is
done.

At about the same time, Thomson saw the light. Some
theoretical work by Rankine on the adiabatic expansion
of steam, together with the observation that high-pres-
sure steam escaping from a safety valve does not scald
because it comes out dry, abruptly convinced Thomson
that steam could be heated by friction. It is difficult to
see why this should suddenly have appeared so conclu-
sive to him when Joule had been using the same con-
cepts for seven years. However that may be, Thomson
soon embarked on a long paper, stating the two laws
explicitly and independently, one ascribed to Joule and
the other to Carnot and Clausius. The introductory his-
torical account was of course quite biased and incom-
plete; it was the forerunner of those which are usually
written today. This paper, with the appendixes which
were added at various times, included the thermoelec-
tric relations and a discussion of elasticity.

In 1850 Clausius wrote that the “internal work V"

has the properties which are commonly assigned to the
total heat, of being a function of V and T and of being
therefore fully determined by the initial and final con-
ditions of the gas.

He treated U with the same mathematical techniques as
Laplace and Poisson and Clapeyron had applied to q.
The quantitiy HdQ/T began to appear quite early in
papers by Thomson and Clausius, but it was not till
1865 that Clausius deemed it worthy of special defini-
tion. He wrote:

We can say of it that it is the transformation content
of the body, in the same way as we say of the quantity
V that it is the heat and work content of the body

and coined the name entropy for it. The mathematical
methods of the caloric theory were finally recovered;
thermodynamics today still bears the impress of La-
place and Poisson, just as surely as electrostatics.

Conclusion

THE conventional description of the caloric theory,
as a qualitative model of heat processes which had
to be abandoned as soon as Rumford did his cannon-
boring experiments, is obviously untrue. The difficulty
encountered by the proponents of the dynamic theory
of heat was that they had first to break the strangle-
hold of a glib mathematical formulation, a method
which could make a sufficient number of correct pre-
dictions to give the illusion of being the whole truth.
But probably this was a necessary stage in the develop-
ment of the subject, since it did after all allow the
formulations to be worked out. After that, there just
remained the enormous intellectual difficulty of pro-
posing two laws where instinct said that only one ex-
isted; when that was done the theory of heat was virtu-
ally complete.

*-

BEFORE OUR TIMES

25

A Sketch
for a History

THE KINETIC THEORY

OF GASES

By E. Mendoza PHYSICS TODAY / MARCH 1961

THE ideas that solids are composed of compact
arrays of atoms, while gases are composed of
atoms or molecules in very rapid translational
motion, are so obvious that we accept them nowadays
without question; in teaching textbooks they are stated
as if they were axioms. In its most elementary form,
without any sophisticated calculations about the dis-
tribution of velocities, with only the one assumption
that the impacts of the molecules on the walls of the
containing vessel produce the pressure, a very simple
calculation gives the equation

pV — ysmNc2 (1)

where m and N are the mass of a molecule and the
number per unit volume, and c is a velocity; p is the
pressure and V the volume of the gas.

This formula poses something of a historical puzzle.
For comparing it with pV = RT, there is the strong
implication that the temperature — and therefore the
heat content of a gas whose specific heat is constant
with temperature — is proportional to the kinetic energy
of translation of the molecules, and hence that heat is
a form of motion. It is stated in every textbook that
this kinetic theory originated with Daniel Bernoulli in
the middle of the eighteenth century. But it is equally
well known that the dynamical theory of heat was not
accepted till a whole century later. On the face of it,
therefore, scientists seem to have been singularly obtuse
not to have recognized the straightforward implications
of Eq. (1) for so long.

But in reality it seems that the kinetic theory of
gases is quite a modern development. It was not at all
obviously correct; it was not accepted into physics until
it had overcome some formidable opposition. The out-
line of the story will be given here.

The Static Theory oj Gases

IT is quite true that Bernoulli did give an excellent
account of the kinetic theory in his book on hydro-
dynamics published in 1738. But I have never been
able to trace a single reference to this theory in any
paper or book published in France or England during

E. Mendoza is senior lecturer in physics at Manchester University,
England. His “Sketch for a History of Early Thermodynamics” ap-
peared in the February 1961 issue of Physics Today, p. 32.

the first half of the nineteenth century; it was piously
disinterred in 18S9. The influence that Bernoulli’s kinetic
theory had on other physicists during the critical period
was nil; it might just as well never have been written.

Most scientists in France and Britain adopted instead
the static theory of gases. According to this, the forces
which held atoms together in a solid were attractive
forces which gave the solid its cohesion, but in a gas
these changed into repulsions. The atoms tried to get as
far from one another as they could, and this purely
static effect produced the pressure. A gas was therefore
merely a highly expanded solid; except for accidental
effects like convection, the atoms in a gas were quite
stationary.

This theory originated with Newton but Laplace re-
fined it in several authoritative papers published around
1824. The origin of the repulsive forces was taken to
be the short-range repulsions of the caloric atoms inside
the gas molecules. Lengthy calculations showed that
whatever the law of force

Pressure = (constant) p2 q 2

where p was the gas density, q the charge of caloric
in each molecule. Considering the dynamic equilibrium
of emission and absorption of the caloric and taking
the temperature to be proportional to the density of
caloric atoms in transit, he found

Temperature = (constant) p q2

and hence the gas laws followed. These papers are
deeply impressive, but they leave the nasty impression
that the abstractness of the mathematics was a sign
of decadence. The fact that the quantity of heat ap-
pears squared in both these formulae seems to conceal
some basic confusion, hidden somewhere under the
mathematics.

In England Newton’s theory was widely taught, but
not everyone was in agreement. When Davy wrote
his Elements of Chemical Philosophy in 1812, he in-
clined quite strongly towards the dynamical theory of
heat and proposed that in solids the motion was a
vibration or undulation of the atoms, but that in gases
the atoms also rotated about their axes. He seems to
have had a glimmering of the idea of the partition of

26

HISTORY OF PHYSICS

energy between the rotational and vibrational modes,
and to have tried to explain the latent heat of boiling
in this way. The idea that gas atoms revolved on their
axes made a great impression on Davy’s contemporaries.
For combined with the orthodox static theory of gases
it allowed a precise model to be made of the origin of
the repulsive force between gas molecules — namely the
centrifugal force of the revolving atomic atmospheres.
This idea was later taken up by Joule and Rankine.

In this discussion it is important to realize that there
were several possible concepts of atoms. They could be
point centers of force — the forces could have a finite
range or could extend an infinite distance — or they
could be particles with definite shapes. There were
difficulties in imagining the collisions between atomic
particles to be perfectly elastic, however; for a body
could deform elastically only if its parts moved rela-
tively to one another, whereas an atom was usually
held to be an indivisible elementary particle and there-
fore without substructure. For the same reason, Davy’s
idea of atoms with revolving atmospheres offended
some purists. But I get the impression that different
scientists had quite private views on such questions
which they rarely bothered to state explicitly.

Herapath’s Hypothesis

JOHN Herapath, a self-taught schoolmaster from
Bristol, originated the kinetic theory of gases as we
know it. He had a genius for distorting irrelevant facts
to fit incorrect theories; but if we take the cruel but
realistic criterion that the most important scientists
are those whose ideas have influenced others, who have
proposed theories which are in the main stream of
scientific thought, then Herapath is among the most

The first practical steam carriage to ply
along English roads, between Bath and
London, in 1829. John Herapath is up
front. (Information kindly supplied by
Spencer D. Herapath of London.)

important; the kinetic theory of gases is firmly founded
on “Herapath’s hypothesis”.

He began by noting a small discrepancy in some
observations on the motion of the moon, and proposed
that Newton’s constant of gravitation was not in fact
a constant but varied with the temperature of the
planet concerned. Thus he was led to a study of New-
ton’s model of the gravific ether, the gas whose pres-
sure produced the gravitational force — though Newton
himself had of course stressed that the model was not
very important. Hence Herapath was led to study the
properties of gases in general. He tried to deduce them
from the caloric theory and made no progress; then he
accepted Newton’s theory of static atoms with mutual
repulsions but could not see

. . . how any intestine motion could augment or
diminish this repulsive power. But it struck me that if
gases were made up of particles or atoms mutually
impinging on one another and on the sides of the
vessel containing them . . .

the theory would be more simple, consistent, and easy.
After very many pages of quite impenetrable verbal
arguments, exhibiting an astonishing confusion about
the meaning of the law of conservation of momentum,
he eventually reached a set of propositions which are
roughly equivalent to Eq. (1) above.

He then gave experimental proofs that his hypothesis
was correct. In a thermal mixing experiment in a
calorimeter, he said, quantity of motion was conserved;
and quantity of motion, as everyone knew, was mo-
mentum. Since momentum depended on the first power
of the velocity whereas Eq. (1) implied that the abso-
lute temperature varied as the square, he predicted
that when equal masses of the same substance at
absolute temperatures T1 and T„ were mixed, they
would reach equilibrium at T3 where

+ VTl = 2 VT3.

Water at 0°C and 100°C should reach equilibrium not
at 50°C but at 48°C. He could not perform the experi-

BEFORE OUR TIMES

27

ment himself for lack of good thermometers, so he
searched the literature. Crawford, he found, had deter-
mined the equilibrium temperature to be 50.0°C; but
this result, said Herapath, was the expected one, it was
therefore suspect and should be rejected. (Actually it
is within 0.05° of the correct value.) De Luc, on the
other hand, had found 48.3 °C. This confirmed Hera-
path’s theory. But there was another proof, equally
convincing, that his theory of gravity was correct. For
it was well known that the acceleration of gravity at
the earth’s surface varied from equator to pole in a
way which did not conform to the known ellipticity of
the earth. But Herapath could now explain this in terms
of the influence of the temperature at the two latitudes
on Newton’s “constant” of gravitation. Again his theory
was in agreement with observation.

These papers were published in 1821, to be followed
by long drawn-out disputes, attacks, refutations, and
denials. But after they died down, there were three
rival theories of gases — Newton’s static theory, Davy’s
rotational model, and Herapath’s hypothesis.

Joule and Others

IF Herapath remains a comic figure in spite of his
real achievement, John James Waterston was a man
whose genius was dogged by tragic ill luck. In 1843,
while a schoolteacher for the East India Company in
Bombay, he had a book published in Edinburgh —
anonymously — entitled Thoughts on the Mental Func-
tions, an attempt to explain human behavior in mathe-
matical and physical terms. In a note at the end, he
gave a full and accurate account of the kinetic theory

Waterston as he appeared at the age of
46. (Courtesy Oliver & Boyd Ltd. from
The Collected Scientific Papers of J. J.
Waterston, edited by J. B. S. Haldane.)

of gases. But nobody read the book. Two years later
he sent a paper to the Royal Society on the physics
of media composed of free and perfectly elastic mole-
cules in a state of motion; he wrote that he hoped
that “although the fundamental hypothesis [of perfect
elasticity] is likely to be repulsive to mathematicians,
they will not reject it without a fair trial”. But the
referee reported that it was “nothing but nonsense”
and only a short abstract was published, in another
journal. Waterston not only developed the basic ideas
precisely and was the first to see the relevance of
Graham’s recently published law of the effusion of gases
through small holes, but he also stated the principle
of equipartition of energy, introduced the concept of
the mean free path (the “impinging distance”) and
proposed modifications of the model to represent im-
perfect gases. But his work was passed over and his
influence on the main stream of science was negligible
compared with that of the gregarious Mr. Herapath.

Joule favored Davy’s rotational hypothesis at first.
In a paper on electrolysis (1844) he spoke of revolving
atmospheres of electricity and later he used the same
idea to explain radiation. In his paper on the rarefaction
of air he said that the centrifugal force of the re-
volving atmospheres was the sole cause of the expansion
of a gas when the pressure was removed. But his main
interest was to calculate the specific heats of gases.
In one of his notebooks is to be found the rough draft
of a lecture in which he drew a block of a substance

. . . containing a number of atoms each of which
revolves rapidly on its axis in the direction of the
hands of a watch. Suppose now a number of fine cords
to be rolled round each of these atoms and to pass
over a wheel. It is evident that the force of the atoms
will be diminished in winding up the weight W. This
diminution of the velocity of the atoms is what we
generally call a diminution of temperature. . . .

But shortly afterwards he realized that both rotational
and translational motion could give the result that the
vis viva of the atoms was proportional to the heat con-
tent. In 1848 he wrote that since Herapath’s hypothe-
sis was simpler, he would use it in preference to Davy’s.
He calculated the molecular velocities in several gases
and also some specific heats. These were the first
definite numbers ever to emerge from the kinetic
theory of gases (except for those in Waterston’s pa-
pers). Thus the kinetic theory of gases and the dy-
namical theory of heat were developed at the same time
and largely by the same people.

Rankine developed the rotational (or vortex) theory
to its highest refinement shortly after this. The essence
of his method was to divide up each revolving atmos-
phere into concentric shells, typically of area 4t tt2

J

28

HISTORY OF PHYSICS

and acted upon by a centrifugal force of the type
mc2/r; the pressure p was therefore of the type
7nc'-/4nr'i. The total volume V of N such atoms was
|-7r r3 N. Substituting, one arrives again at Eq. (1).
Rankine extended this to arbitrarily shaped vortices and
again reached the same result — as must always be for
any form of motion because of the implicit assumption
of the equipartition of energy. This was an interesting
situation, for no experiment could ever decide which
was the correct model. But within a few years Hera-
path’s hypothesis gained almost universal acceptance.
Even Waterston managed to get a paper published on
it in 1851. The German scientists Kronig and Clausius
evolved just the same ideas independently in 1856 and
1857 (though Clausius certainly knew of Joule’s results
on molecular velocities). Two years later, a German
translation of Bernoulli’s old paper was published.
Within a short time even British scientists were writing
of “Bernoulli’s theory lately revived by Mr. Herapath”
and it was not long before Herapath’s name was almost
forgotten.

The vortex model persisted for a long time, however,
in various guises. Maxwell dismissed it for an ordinary
gas, in preference to Herapath’s hypothesis, because he
thought the rigidity would be too high. But he used it,
as is well known, as the basis of his model of the
electromagnetic ether. Later still, Kelvin made smoke-
ring models of atoms to explain spectra. His calcula-

tions of the modes of oscillation of such systems have
a very modern sound.

Conclusion

* I ''HE outstanding feature of this story is that — like
the dynamical theory of heat — the kinetic theory
of gases had first to break the grip of an abstruse and
authoritative mathematical theory before the simple
basic physical ideas could be accepted. These difficulties
should, perhaps, be presented in their proper perspec-
tives in our teaching textbooks.

Above all, these episodes accentuate the problem of
communication in science. The records of the Royal
Society and the French Academy of Sciences are blotted
again and again by the rejection of outstanding dis-
coveries. On the other hand, a hypothesis like Hera-
path’s, published in a journal with less stringent
refereeing, was embedded amid so much nonsense-
writing that it took the instinct and genius of a man
like Joule to uncover the one idea worth preserving.
When the amateur historian descends into the stacks'
of a library he can contemplate the yards and yards
of dusty volumes, records of decades of busy scientific
activity. On the average, perhaps one short paragraph
out of the huge output of any one year was really
worth writing. Scientific researches are like fishes’
eggs — only one in thousands ever reaches maturity.
It is a chastening thought.

A sketch (drawn sideways
to save space) from one of
Joule’s private notebooks.
It illustrates his idea of
the rotating atom theory.

BEFORE OUR TIMES

29

Rowland’s physics

Of the three most eminent US physicists of the late nineteenth century,
Gibbs, Michelson and Rowland, it was the “doughty knight of Baltimore” who
had the broadest impact, setting the pace for the golden age of US physics.

John D. Miller

PHYSICS TODAY / JULY 1976

“Those were the days,” reminisced Daniel
Gilman, the President of The Johns
Hopkins University, “when scientific
lecture-rooms in America gloried in
demonstrations of ‘wonders’ of Nature —
‘the bright light, the loud noise, and the
bad smell.’ Rowland would have none of
this.” The Johns Hopkins physicist thus
characterized was Henry Rowland, whose
contributions — particularly those in
spectroscopy and electromagnetism —
secured him a high place in the ranks of
nineteenth-century physicists.1

Neither experimental nor theoretical
physics was widely practiced in the
United States during the middle of the
nineteenth century. The popular study
was natural history, a subject for which
the bountiful Nature of a young and
largely unexplored country offered a col-
lage of unknown plants, animals and
geological patterns to investigate. The
description of such novelties required
neither mathematical nor other formal
training, and although professionals ap-
peared, the field was particularly attrac-
tive to dilettantes and amateurs.2 But
the logic and mathematics of exacting
physical investigations lay beyond the
reach of amateurs. It was not surprising,
therefore, that papers on natural history
filled the American Journal of Science,
the leading science publication in the
United States and one read extensively
abroad — or that the mathematics so sel-
dom encountered in the Journal’s pages
appeared puerile in comparison to Euro-
pean standards.

However, in the latter half of the cen-
tury at least three physicists in America

John D. Miller is an associate professor at, and
associate director of, the Lawrence Hall of
Science of the University of California, Berkeley.

practiced their mathematics as well as
their science at a level equal to the best of
their European colleagues: J. Willard
Gibbs, Albert Michelson and Rowland.
All three men were anomalies in nine-
teenth-century America.

Of these three it was Rowland who, in
terms of laboratory investigations, set the
most influential standards for physics
research, particularly through his precise
instrumentation. Although Michelson
became well known, particularly when his
ether experiments were found to corro-
borate the Lorentz-Fitzgerald contraction
hypothesis, this did not come until much
later. Furthermore, recent findings have
refuted the idea of a generic relationship
between Michelson’s work and Albert
Einstein’s postulates of 1905.3

Rowland, in contrast, had completed
major experiments in magnetism and
electricity, and his diffraction gratings
and Sun-spectrum photographs were, in
the 1880’s, distributed and acclaimed
throughout the world. Later, in 1894,
Michelson himself even turned to Row-
land for advice concerning the suitable
outfitting of a new physical laboratory at
the University of Chicago. As for Gibbs,
although his work was of the highest
quality, it was all theoretical — it is
doubtful that he had ever set foot inside
a laboratory. In the end it was Rowland
who set the pace in US laboratory physics
in the last quarter of the century.4

The education of a civil engineer

When Rowland was born in 1848 he
became the only son in a family of five
children. When he was eleven, his posi-
tion of responsibility was underscored by
the death of his father, a Protestant the-
ologian. This occupation had been fol-
lowed by three generations of Rowland

males, all of whom are reported to have
possessed exceptional intellects and
dominant personalities. In fact the ear-
liest, David Rowland (1719-94) was from
his Providence pulpit such a zealous de-
fender of his country against foreign op-
pression that during the Revolutionary
War he was forced to flee the city, escap-
ing with his family up the Connecticut
River in darkness through the midst of a
surrounding British fleet.

Rowland’s mother Harriet expected
him to follow family tradition and en-
rolled him, at thirteen, in classical studies
at New Jersey’s Newark Academy. But
Henry was more interested in mechanics
and electricity, as a small pocket notebook
that he began in 1862 records. Found
here are accounts of the things he made —
electromagnets, induction coils, galva-
nometers and electric motors. Scientific
studies had not yet won prominence in
American education, however, and ac-
cording to Samuel Farrand, the Academy
headmaster, a scientific education to
Harriet Rowland “seemed like throwing
away her boy.”

Rowland suffered through three years
of Latin and Greek, finally writing in July
1865 that classical studies were “horrible,”
declaring “ ‘Non feram, non patiar, non
sinam’ [I will not bear, I will not suffer, I
will not tolerate] is a sentence which just
expresses my condition.” He petitioned
his mother to study science. Eventually
she relented, and when Rowland was 17
he enrolled in the Rensselaer Techno-
logical Institute in Troy, New York.

The “scientific course” was largely
oriented toward practical applications
and led to a civil-engineering degree. The
school also trained mechanical and hy-
draulic engineers as well as architects and
superintendents of gas and iron works.

30

HISTORY OF PHYSICS

ROWLAND

At Rensselaer Rowland studied math-
ematics through the calculus of variations,
but spent most of his time with apparatus
that he constructed and operated in his
boarding-house room. His letters home
were filled with descriptions of galva-
nometers, electrometers and a Ruhmkorff
coil that would, as he wrote his sister
Jennie, “charge and discharge a Leyden
jar twenty times a second or more.” He
was very active in the school’s scientific
club, reading papers in 1868 on spectros-
copes, the mechanical equivalent of heat
and tests of his induction coils.

In the fall of 1876, his third year, Row-
land arranged his classes so as to spend all
his mornings uninterrupted on his ex-
periments. He also began to keep records
of his work in bound notebooks. Entries
included sketches of gold-leaf electros-
copes, the origin of electricity produced by
the contact of water and heated metal, the
upward force of wind necessary to support
a man in flight with “wings” twenty feet
in length, and the change in the position
of the apparent poles of a horseshoe
magnet when an armature was placed
across its legs.

The next year brought records of much
more serious studies — particularly in
numerous references to one special source
of ideas: The Experimental Researches
in Electricity of Michael Faraday is the
first entry in a list of scientific books
contained in one notebook. Another
two- volume notebook of 1868 contains
more than a dozen references such as
“Notes from Faraday’s Experimental
Researches in Electricity” and “Thoughts

suggested by the reading ... of Faraday.”

Faraday’s ideas, as recorded in these
volumes, eventually provided the basis for
two of Rowland’s major experimental in-
vestigations: the magnetic analogy to
Ohm’s Law and the magnetic effect of a
moving electrical charge. His interests
were thus not limited to civil engineering;
he wrote to his mother in May 1868:
“You know that from a child I have
been extremely fond of experiment;
this liking, instead of decreasing, has
gradually grown upon me until it has
become a part of my nature and it
would be folly for me to attempt to
give it up . . . I intend to devote my-
self hereafter entirely to science — if
she gives me wealth I will receive it as
coming from a friend but if not I will
not murmur.”

The magnetic analogy to Ohm’s law

After his graduation from Rensselaer in
June 1870 with the degree of Civil Engi-
neer, Rowland could not find a position in
experimental science. He spent his time
on a series of magnetic researches con-
ducted at his mother’s Newark home.

These experiments were originally in-
tended to determine the distribution of
magnetism in several iron and steel bars.
Rowland soon found it difficult, however,
to interpret his measurements. At this
time little was accurately known about
the effects of various media and geometric
configurations on the transmission of
magnetic forces. Experimenters such as
Sir William Harris, William Sturgeon, Sir
James Joule, Heinrich Lenz and Joseph

Henry had studied isolated factors, but
their experiments had produced no single
model of magnetic action that simulta-
neously took into account the shape of the
core, its material composition and the
arrangement of the energizing coil.

By using detection coils that could be
quickly reversed by physical means, wired
to a galvanometer of his own design,
Rowland began a very accurate mapping
of the magnetic fields produced by direct
electric currents, checking alignments
with his rifle sights. The method de-
pended upon obtaining a reversal time
that is a small fraction of the natural os-
cillation period of the galvanometer.

As he traced Faraday’s lines of force in
various materials he experienced diffi-
culty in interpreting his measurements,
for the configuration of the lines appeared
to shift as the current in the electromag-
nets was varied. The shift was only a few
per cent but it was enough to upset Row-
land’s venerated sense of precision. His
interest was aroused to seek a theoretical,
mathematical model of the phenomena.

For a physical model to analyze, Row-
land turned to the analogy between elec-
tricity and magnetism that Faraday had
postulated in his diary. The idea in-
volved Gymnotus electricus, an eel hav-
ing electric organs concentrated along its
body and tail. Using his bare hands to
estimate intensities, Faraday in 1838 had
studied the distribution of electricity
surrounding the eel during its moment of
discharge, sketching the action as shown
in figure 1 . F araday pictured the physical
lines of electric force as continuous
through the cells of the eel and its sur-

The electric action of an eel, as Michael Faraday
sketched it in his notebook in 1838. Estimating
intensities with his bare hands, Faraday found at
the moment of discharge that “every part of the
water" is filled with a current from the front to
the rear of the eel. From this Rowland drew an
analogy to the lines of force surrounding a
bar magnet. Figure 1

BEFORE OUR TIMES

31

rounding medium, “for they form con-
tinuous curves like I have imagined within
and without the magnet.” The three-
dimensional aspect of the analogy repre-
sented characteristic Faraday brilliance.5

In a notebook of 1872 Rowland cited
Faraday’s Gymnotus work, but evolved
the idea further, using the well known
nineteenth-century telegraph circuit.
The imperfect insulators of a telegraph
line correspond to lines of magnetic force
in a medium surrounding a magnet; the
galvanic cell represents the source of the
lines of force, and the analog of the hori-
zontal wire is the conduction of the lines
within the magnetic material itself.

Having pictured the circuit for one
electric cell of the eel, Rowland imagined
a distributed set of such cells, as shown in
figure 2a, corresponding to a series of
short bar magnets laid end to end as
shown in figure 2b. Rowland in 1873
added the effects of the driving force of
each cell to obtain the following equa-
tions, which describe the distribution of
Faraday’s lines of force in and near a long
magnetic bar:

Q.=

Q' =

M

1 - A

2 VRR’ (APb - 1)

(rb _ 1

(erx - er(b~xi)

M

(A

:rb

M l — A

2 RAtrb - 1

1 )(VRR'-s') r

(erb + 1 - trx - (Ab-x))

In these equations r = (R/R')1/2,
ARR' + s'

A =

/RR’

and

R = resistance to lines of force of 1 m of
length of bar

R' = resistance of medium along 1 m of
length of bar

Q' = lines of force in the bar at any
point

Q, = lines of force passing from the bar
along a small distance l
e = base of Napierian logarithms
x = distance from one end of the helix
b = length of helix

s’ = resistance, at the end of the helix, of
the rest of the bar and the medium
M = magnetizing force of the helix.

These complex exponential forms were
obviously far from Ohm’s simple propor-
tionality law. However, Rowland went on
to study the predictions of his equations
for the center of a long thin magnet, for
which, from his observations of the lines
in the media surrounding the magnet and
from symmetry considerations, he ex-
pected the lines to assume homogeneous
paths and his equations to reflect this
simplification. Rowland did not publish
the details of the algebraic transformation
of these equations under these limiting
conditions. At the center, x = 6/2, of any
magnet, the number of lines, Q„ passing
along the bar at some small distance
clearly vanishes, since the factor on the
right of the first expression becomes zero

A telegraph circuit provided Rowland with a heuristic link between Faraday’s electric eel and a bar
magnet. Sketch a, taken from one of Rowland’s notebooks, shows a nineteenth-century telegraph
circuit with distributed galvanic cells added. The series of short bar magnets shown in b completes
the analogy, which led to a magnetic equivalent of Ohm’s law. Figure 2

there. On the other hand, the number of
lines in the bar does not vanish at this
point but equals

Q' =

1 - t-rb M

(A - t-rb)(VRR’ - s') 7

M 1 - A
2R A — f ~rb

(t~rb + 1 - 2e~rbl2)

For the case of the infinitely long bar,
6 — ► , Rowland found that this equation

reduces to

Thus in the center of the magnet the
number of lines passing through the
magnetic medium was proportional to M,
the magnetizing force in the magnet, and
inversely proportional to R, the resistance
to these lines of force. He had therefore
found a magnetic analogy to Ohm’s law
for electric circuits.6

To use this simplified formula for
measuring the magnetic properties of

different metals Rowland constructed
toroidal magnets. In this geometry the
lines of force closely approximate those
observed at the center of a long bar. An
early Rowland ring is shown in figure 3.

The above equations were the product
of several experiments begun three years
earlier. Rowland had repeatedly received
rejection notices from the editors of the
American Journal of Science, who finally
admitted that they simply did not un-
derstand his mathematics. But before
receiving this explanation Rowland sent
his 1873 paper directly to James Clerk
Maxwell, whose treatise of that year had
contained a general theory of magnetism
from which Rowland’s equations could be
derived. This congruency could have
been expected: Both men had started
with Faraday’s ideas. Maxwell was much
taken by Rowland’s work and arranged
for immediate publication in the Philo-
sophical Magazine in England.

In 1875 Rowland found an appoint-
ment at Rensselaer, but was given no de-

In a toroidal magnet the lines of force are similar to those at the center of a thin bar magnet. The
first Rowland ring is shown in a dated entry from Rowland’s notebook. Figure 3

32

HISTORY OF PHYSICS

Rowland-Hutchinson charge-convection apparatus seen from above, in an 1889 photo. The
question Rowland asked was whether the mere motion of a charge could generate magnetic effects
similar to those of a current in a wire. His answer, yes, proved hard to confirm. Figure 4

cent laboratory in which to carry out exact
experimental research. That year
through a relative he met Gilman, who
had been appointed President of the
newly founded Johns Hopkins University.
Gilman saw Maxwell’s letters, thought
them “worth more than a whole stack of
recommendations” and hired the young
Rensselaer engineer to organize a physics
department at Johns Hopkins.

The charge-convection experiment

That summer of 1875, Gilman took
Rowland to Europe to inspect institutions
of science and to visit instrument shops
with a view toward outfitting a physical
laboratory for Johns Hopkins. On his
own, Rowland was Maxwell’s house guest
in Scotland and then crossed to the Con-
tinent, arriving in Berlin in late Octo-
ber.

Rowland had not been impressed by
much of what he saw, reporting that many
shops seemed like “museums of antiqui-
ty” and the laboratories looked as though
the “architect had got the best of the
physicist.” But in Germany he wrote
Gilman,

“You were right when you said I would
find no lack of scientific spirit here
and the apparatus shows it. In Amer-
ica we have apparatus for illustration,
in England and France they have ap-
paratus for illustration and experi-
ment, but in Germany, they have only
apparatus for experimental investiga-
tion. Our country is hardly ripe for
the latter course though I should like
to see it pursued to the best of our
ability.”

Caught up in this spirit, Rowland ap-
plied for a general course of study in the
university laboratory at Berlin under
Hermann Helmholtz. The distinguished
German physicist’s reply was prompt and
negative, citing crowded conditions.

Not giving up, Rowland wrote to
Helmholtz again, this time proposing as
specific experiments either an extension
of his magnetic researches or a plan that
Rowland had recorded in his Rensselaer
notebook of 1868:7

“The question I first wish to take up is
that of whether it is the mere motion
of something through space which
produces the magnetic effect of an
electric current, or whether those ef-
fects are due to some change in the
conducting body which, by affecting
some medium around the body, pro-
duces the magnetic effects.”

Rowland and Maxwell had discussed
these ideas the previous summer, and
Rowland told Helmholtz, “Maxwell as-
sumes that the last case will produce
magnetic effects although he has since
told me he had no reason for the as-
sumption.” In the 1873 Treatise, Max-
well did in fact indicate his “supposition
that a moving electrified body is equiva-
lent to an electric current” but did not
give his reasons.

This time Helmholtz was interested
and had a storage room cleaned out in the
basement for Rowland. Months earlier
Helmholtz had been investigating the
possibility of convection currents related
to his and Franz Neumann’s potential
theory of magnetic actions, which he de-
scribed as “open” circuits. Did the dis-
charge of arc observed between discon-
nected wires, Helmholtz wondered, ac-
tually complete the circuit, accompanied
by magnetic effects?

Rowland set up a single gilded ebonite
(vulcanite) disk, 21 centimeters in diam-
eter, to revolve about a vertical axis 60
times a second. He reversed the polarity
of the electrification while observing the
reflection of a beam of light reflected from
a mirror attached to a delicate magnetic
astatic-needle system. The mirror was
placed on a thread between two compass
needles aligned with poles opposed to
cancel the effect of the Earth’s magne-
tism. The disk revolved on a plane be-
tween the needles. Figure 4 shows an
1889 version of the apparatus. After
several weeks of trials he reported a dis-
tinct deflection of the beam by several
millimeters, noting that this “qualitative
effect . . . once being obtained, never
failed.” He was reporting a magnetic
force only about 1/50 000 of that of the
Earth’s horizontal component in Berlin.

Not stopping at this qualitative mea-
surement, Rowland went on to compute
the expected magnetic force to compare
it to measured values. To do this he had
to assume some value for Maxwell’s v, the
ratio of electromagnetic to electrostatic
units — the constant Maxwell had postu-
lated to be equal to the velocity of light.
Rowland assumed a value of 288 million
m/sec, as measured by Maxwell, to pro-
duce the Table on page 43 from 62 read-
ings of individual deflections.

The difference between expected and
measured values of force, Rowland noted,
was 3, 10, and 4 per cent respectively with
Maxwell’s value for u. He observed,
however, that the “value v = 300 000 000
meters per second, satisfies the first and
last series of the experiments best.”

This mechanically brillant experiment
cost only about fifty dollars. Many were
to attempt to repeat it in a variety of
forms — and be frustrated — in the next 25
years. It was Maxwell himself who be-
stowed the laurels, writing in serio-comic
verse,

The mounted disk of ebonite

Has whirled before, nor whirled in
vain;

Rowland of Troy, that doughty
knight,

Convection currents did obtain
In such a disk, of power to wheedle,
From its loved North the subtle
needle.

‘Twas when Sir Rowland, as a stage
From Troy to Baltimore, took rest
In Berlin, there old Archimage,

Armed him to follow up this quest;
Right glad to find himself possessor
Of the irrepressible Professor.

But wouldst thou twirl that disk once
more,

Then follow in Childe Rowland’s
train,

To where in busy Baltimore

He brews the bantlings of his
brain . . .

Back to Baltimore

When Rowland returned to Baltimore
from Europe in the spring of 1876 he told
Gilman, “Give me time and apparatus
and if our University is not known, it will

BEFORE OUR TIMES

33

Rowland in a self-portrait, about 1882. Centrally placed in his bachelor apartment was the bronze
horse Rowland bought with the prize money that was awarded to him for his precise measurement,
in 1880, of the mechanical equivalent of heat. Figure 5

not be my fault.” Rowland wanted re-
search apparatus “ not for the illustration
of lectures.” He argued that, although it
was sometimes possible to produce good
work with poor apparatus — just as it is
possible to cut down a tree with a pen-
knife— there is work that can not possibly
be done without calling to our aid all the
resources of mechanics. To this class, he
asserted, belong ‘‘many of the higher
questions in mathematical physics.”

Gilman showed him two former
boarding houses in downtown Baltimore
that were to serve as temporary labora-
tories. Rowland said that all he needed
in one of the buildings was the back
kitchen and a solid pier built up from the
ground “to sustain such instruments as
require steadiness.”

His intentions were to carry out a series
of measurements of basic physical con-
stants. The philosopher, logician and
meteorologist Charles Peirce visited
Baltimore in 1878 and was critical of
Rowland’s plans. But Rowland went
ahead anyway, beginning a new determi-
nation of the mechanical equivalent of
heat. This massive project led in 1880 to
a 125-page report, including subsidiary

investigations in thermometry and calo-
rimetry. The research, a paradigm of
precise measurement, won Rowland the
Venetian Prize in 1881 and, recommend-
ed by Peirce, an honorary doctoral degree.
In the background of Rowland’s self-
portrait, figure 5, the bronze horse that he
purchased with the prize money can be
seen.

Rowland also carried out precise mea-
surements of Maxwell’s ratio of units at
this time, again as a test of the electro-
magnetic theory of light. He used a
spherical condenser that had been ma-
chined with great precision to provide a
known capacitance. Its stored charge in
turn was passed through a calibrated
galvanometer.

The first of these measurements looked
promising, Rowland wrote to Maxwell in
April 1879: “I believe the experiment is
a link in the proof of your theory seeing
that the result is, by the first rough cal-
culation, 299 000 000 meters per second,
though the corrections may amount of %
per ct. or so.” But subsequent measure-
ments produced a v of 297 900 000 m/sec,
a value that decreased with the number of
discharges employed; this discouraged

Rowland initially from publishing his re-
sults.

A third constant related to v was the
value of the standard resistance, the ohm.
In the electromagnetic system of units
evolved in the latter half of the century,
length/time were interestingly also the
dimensions of resistance. Many mea-
surements of v ultimately depended on
knowledge of the ohm. Rowland was
critical of measurements made by the
British Association and a German group
headed by Friedrich Kohlrausch, dis-
covering arithmetical errors and in-
consistencies through dimensional anal-
ysis. His criticism proved valid, and he
served on several international com-
mittees through the 1880’s, presiding over
the International Electrical Congress in
Chicago in 1893.

It is little known but Rowland had as-
sembled the most elaborate and extensive
set of equipment to be found anywhere in
the world in the late 1870’s and early
1880’s. Physicists at Harvard had in-
ventoried US collections,8 and Rowland’s
student Edwin Hall told Gilman that
Johns Hopkins “would be the loser” if it
exchanged its apparatus with that at
Cambridge University’s Cavendish Lab-
oratory, for example, particularly if “what
belongs to Prof. Rowland personally was
included.”

In 1877, by using superb galvanometers
and an experimental configuration de-
vised by Rowland, Hall measured an
electric potential acting perpendicular to
a line of current flow and to a magnetic
field. A fluid model of electricity was
used throughout Hall’s work, perhaps the
last productive use of this model leading
to fundamental electrical laws. In 1894
Rowland disclosed the extent to which he
had been involved in Hall’s work, telling
George Fitzgerald that the convention
experiment, “. . . together with that of Mr.
Hall [Hall effect] which was really my
experiment also, were made to find the
nature of electric conduction. Indeed I
had already obtained the Hall effect on a
small scale before I made Mr. Hall try it
with a gold leaf which gave a larger effect.
My plate was copper or brass and I only
obtained 1 mm deflection. Mr. Hall
simply repeated my experiment, accord-
ing to my direction, with gold leaf.”
Rowland’s colleague Joseph Ames wrote
in an account of the period, “There have
been several striking cases where it might
have seemed to an impartial observer that
Rowland’s name should have appeared on
the title page.”

Magnetic force due to a rotating charge.

Series I Series II

Measured magnetic force 0.000 003 27 0.000 003 17

(horizontal component)

Computer magnetic force 0.000 003 37 0.000 003 49

(horizontal component
compound using Maxwell's
value of v)

Series III

0.000 003 39

0.000 003 55

“Magnifique” gratings

Another major line of Rowland’s study
was spectroscopy. Before 1881, the
problem of ruling an optical grating of
high resolution, yet free from large peri-
odic errors in spacing, had been solved
only partially. With his sense of precision
mechanics, Rowland became interested
in the critical worm screw that advances

34

HISTORY OF PHYSICS

the metallized glass plates under an os-
cillating diamond scriber. Periodic errors
in the screw resulted automatically in
grating errors. Rowland invented a
method of grinding screws, submerged in
water, over a three-week period.9 A rul-
ing engine employing the new screw de-
sign was completed in 1882. The figure
on page 26 of this issue of PHYSICS
TODAY shows Rowland with one of his
ruling engines. At about this time Row-
land also invented the concave grating,
which eliminated the need for auxiliary
telescopes or other optical accessories for
observing the spectrum under study.

Rowland, accompanied by his colleague
John Trowbridge, took sample gratings to
the Paris electrical conference of 1882.
Trowbridge reported on the reactions of
French physicist E. E. Mascart, Sir Wil-
liam Thomson and Kohlrausch:

“It is needless to say that they were
astonished. Mascart kept muttering
‘superb,’ ‘magnifique.’ The Ger-
mans spread their palms, looked as if
they wished they had ventral fins and
tails to express their sentiments . . .
We left [Paris] with the feeling that
there was little to be learned there in
the way of physical science, and hav-
ing sent for the above scientists as her-
alds to proclaim the preeminence of
American diffraction gratings . . .”

In England Rowland told an equally en-
thusiastic audience, “I have ruled 43 000
lines to the inch and I can rule one million
to the inch, but what would be the use, no
one would ever know that I had really
done it.” Trowbridge wrote that there
was much laughter at this: “This young
American was like the Yosemite, Niagara,
[the] Pullman parlor car; far ahead of
anything in England ...”

There was great demand for Rowland
gratings, which Johns Hopkins distrib-
uted at cost throughout the world. One
of special note went to Pieter Zeeman,
who used it in 1897 to observe the mag-
netic widening of the two D lines of the
sodium spectrum. Figure 6 shows a
spectrometer in use in Rowland’s own
laboratory.

Distractions from pure science

In 1890 Rowland, then 42, was married
and discovered through a life-insurance
examination that he had diabetes, which
was incurable at that time. He was given
ten years to live.

Until his marriage Rowland had rarely
worked on any commercially related sci-
entific work. (Once, in 1879, he had
tested the efficiency of Edison’s newly
invented electric light.) Nor had he filed
patents on any of his laboratory-appara-
tus inventions. But when Rowland’s
children were born in the early 1890’s all
this changed.

By 1896 he had filed or received con-
firmation of at least nineteen patent
claims dealing with commercial electrical
equipment. He also spent an immense

Using one of Rowland’s gratings in his own laboratory at Johns Hopkins, about 1885. This pho-
tograph, printed from a glass negative, was taken by gaslight. Figure 6

amount of time on a complicated multi-
plex telegraph system. However, the
telegraph with its delicate synchroniza-
tion system never proved commercially
practical and the company went bankrupt
shortly after Rowland’s death.

A commercial consulting project also

absorbed much of Rowland’s time during
1892-93. He was retained as chief design
consultant for the Cataract Construction
Company, which was involved with the
design of a power-generating plant at
Niagara Falls. The generation and
transmission of electric power on such a

=)

o

>

o

z

UJ

=J

o

LU

RATIO OF UNITS v ( 10s m/sec)

Histograms of historical data. The upper diagram shows the frequency of charge-convection
measurements for values of v, the ratio of electromagnetic to electrostatic units, from Rowland’s
1876 Berlin experiment. The lower histogram, of data taken by Rowland and Cary Hutchinson in
Baltimore in 1889, is much less satisfactory, due to electrical noise. Figure 7

BEFORE OUR TIMES

35

scale had never been attempted, and
Rowland spent most of his time during
that period on the project. When his fe'e
of $10 000 was rejected by Cataract he
brought suit. The jury awarded in his
favor, but it had been an inopportune
time for the physicist to be occupied in
court.

This was the year that Philipp Lenard’s
paper on cathode rays in the free atmo-
sphere appeared; the following year
brought Wilhelm Rontgen’s announce-
ment of a hitherto unknown and myste-
rious form of radiation. To Rowland it
was a disappointing period, in which he
published only two minor electrical pa-
pers.

It was not until 1899 that he again di-
rected basic researches into the nature of
electricity and magnetism on any large
scale. Since his Berlin convection ex-
periments of 1875 there had been nu-
merous attempts to repeat the investiga-
tion, with mixed results. In fact, in 1889
Rowland and one of his students at-
tempted a repetition and obtained much
less satisfactory results than those from
Berlin in 1876. In 1970 I summarized the
two sets of data in figure 7 by recon-
structing the ratio of units v from the raw
data of each set of experiments. The
spurious effect of trolley lines and other
technologies of an electrically noisier age
are apparent in the 1889 data.

The most disturbing of these attempts
was a series of researches conducted late
in the century by Victor Cremieu at the
University of Paris, who could not find
any magnetic effect.

But, for Rowland, the effect discovered
by Zeeman of the sodium D line splitting
could be explained by the convection
equipment. Vibrating, electrified
“matter” within a molecule gripped the
ether. This might produce a magnetic
effect, which interacted with Zeeman’s
externally applied magnetism. Perhaps

the rotating matter of the Earth likewise
retained “a feeble hold on the ether suf-
ficient to produce the Earth’s magnetism
. . .” Late in the decade he therefore de-
cided to undertake new experiments in an
attempt to measure directly an interac-
tion with the ether. At the same time he
directed a new series of charge-convection
experiments.

By Christmas 1900, results from a series
of ether experiments in which a cylinder
wound with 80 meters of wire and re-
volved with great velocity in air appeared
promising and Rowland wrote to reserve
space in the American Journal of Science.
But when the commutator leads were re-
versed, the galvanometer failed to reverse;
he never again attained a steady deflec-
tion. Yet positive results were obtained
from a new series of convection experi-
ments and were reported to Rowland
shortly before his death on 16 April 1901.

The decades of the 1870’s and 1880’s
had been the most productive for Row-
land, but the picture is also clear in the
1890’s of a dying physicist torn between
commitments to science and to family.
Only once did he appear to refer publicly
to his diabetic condition, but then it was
with considerable bitterness and frus-
tration:10

“What blasphemy to attribute to God
[death] which is due to our own and
our ancestors’ selfishness is not found-
ing institutions for medical research
in sufficient number and with suffi-
cient means to discover the truth.
Such deaths are murder. Thus the
present generation suffers for the sins
of the past and we die because our an-
cestors dissipated their wealth in
armies and navies, in the foolish pomp
and circumstance of society and ne-
glected to provide us with a knowledge
of natural laws.”

It was not until 1921 that Frederick
Banting and John Macleod discovered

insulin, sharing the Nobel Prize in medi-
cine in 1923.

My historical research on Rowland began in
1967 through a grant from the Smithsonian
Institution. Archivist Frieda C. Thies (re-
tired) assisted me in organizing Rowland’s
scientific notebooks, which I recovered from
uncatalogued storage at the Johns Hopkins
University in 1968. The interested reader can
find additional technical references in the Isis
articles in reference 1. For a copy of Row-
land's letter to Helmholtz, reference 7, I am
obliged to Christa Kirsten, Archiv Direktor,
Deutsche Akademie der Wissenschaften.

References

(Unless otherwise noted quotations and
notebook citations refer to materials
contained in the Rowland and Gilman
manuscript collections at Johns Hopkins
University.)

1. J. D. Miller, Isis 63, 5 (1972); 66, 230 (1975).

2. Science in Nineteenth Century America,
(N. Reingold, ed.), Hill and Wang, New
York (1964).

3. G. Holton, Isis 60, 2 (1969).

4. Selected Papers of Great American
Physicists, (S. R. Weart, ed.), American
Institute of Physics, New York (1976).

5. Faraday’s Diary, 1820-62 (T. Martin, ed.),
G. Bell and Sons, London (1933), volume
III, page 354.

6. H. Rowland, Phil. Mag. 46, 140 (1873).

7. Rowland to Helmholtz, 13 Nov. 1875, in
the Archives of the Deutsche Akademie der
Wissenschaften, (East) Berlin.

8. J. W. Gibbs, E. R. Wolcott, E. C. Pickering,
and J. Trowbridge, list of [scientific] ap-
paratus, Harvard College Library Bulletin,
volume 11, pages 302, 350 (1879).

9. H. Rowland, “Screw,” reference 4, page 85.

10. H. Rowland, Presidential address to The

American Physical Society, 28 Oct. 1899,
reference 4, page 91. □

BEFORE OUR TIMES

37

Michelson and his
interferometer

Pioneering applications in such diverse fields as
astronomy, atomic spectra and mensuration followed the initial
disappointment over the failure to detect a luminiferous ether.

Robert S. Shankland

PHYSICS TODAY / APRIL 1974

Albert Abraham Michelson was the
first American scientist to win the
Nobel Prize, and his career is one of
the most fascinating in the entire his-
tory of physics. His earliest work was
firmly based on the classical physics of
geometrical optics — in a precise deter-
mination of the velocity of light by an
improved Foucault method. But then
he mastered wave optics and invented
his interferometer, and from that point
on he proceeded to dazzle the scientific
world with a display of the applications
he found for his invention during a ca-
reer that exhibited throughout a
unique pattern of originality and dedi-
cation to physics.

The interferometer came into being
for the specific purpose of measuring
the Earth's motion through the lumini-
ferous ether, a project familiar to gen-
erations of physics students as the
“Miehelson-Morley experiment." Al-
though this single undertaking has
proved important enough to guarantee
Michelson’s place in history, the unex-
pected negative result caused response
at the time to be lukewarm, and this is
not the work for which the Nobel Prize
was awarded in 1907. He was honored
instead for the other applications of his
invention — particularly for his work on
the determination of the length of the
International Standard Meter in terms
of the wavelength of light, but also for
such diverse and pioneering achieve-
ments as the discovery of fine and hy-
perfine structure in atomic spectra and
the first application of interference
measurements in astronomy.

The birth of a concept

Michelson’s invention of this re-
markable instrument, the interferome-
ter— which to the present day plays
important roles in Fourier spectrosco-
py, laser-beam interferometers and the
ring-laser gyro — came suddenly with
but little relationship to his earlier re-
searches on the speed of light.

He had been born in 1852 at Strzelno
in the Prussian province of Posen and
travelled with his parents to frontier
towns of California and Nevada. Then
he made his way with the greatest de-
termination to the Naval Academy at
Annapolis, where he excelled in science
and made his first precise measure-
ment of the speed of light. One will
search in vain in his Annapolis text-
book1 and in his papers and correspon-
dence for clues as to what inspired his
great invention. At Annapolis, and
later, when Simon Newcomb invited
him to collaborate with him at the
Naval Observatory in Washington, Mi-
chelson’s velocity-of-light determina-
tions employed exclusively the meth-
ods of ray or geometrical optics, with
heliostats, mirrors and lenses to pro-
duce intense beams of light; there is no
indication in this period of his concern
or interest in the wave properties of
light or in optical interference.

But in a few weeks in 1880 between
his last velocity of light determinations
with Simon Newcomb in Washington
and his first work in Helmholtz’s labo-
ratory at Berlin (where he had gone on
leave from the Navy for special study
and research), he clearly had mastered
the basic principles of the wave nature
of light and then invented his interfer-
ometer, which is one of the most pow-
erful and elegant applications of the
characteristic interaction between light
waves.

However, two events had occurred in
Washington that bear closely on the
invention of his interferometer. The
first was a letter, dated 19 March 1879,
which James Clerk Maxwell2 had writ-
ten to David Peck Todd at the Nauti-
cal Almanac Office inquiring about as-
tronomical observations on Jupiter’s
satellites suitable for a determination
of the speed of light but which more
importantly, might reveal the Earth’s
motion through the ether of space. In
this letter, which was also studied by

Newcomb and Michelson, Maxwell had
asserted that no terrestrial method was
capable of measuring the speed of light
to the one part in a hundred million
that would be necessary in any labora-
tory experiment to detect the Earth’s
motioq through the ether. Maxwell’s
statement appears clearly to have been
the challenge that the young Michelson
accepted for developing his interferom-
eter specifically to carry out a labora-
tory ether-drift experiment, which he
first conducted in Germany and later
in its final form with Edward W. Mor-
ley at Cleveland.

A second clue showing Michelson’s
shift in interest from ray optics to wave
optics after his study of Maxwell’s let-
ter is suggested by a short paper he
presented to the Philosophical Society
of Washington on 24 April 1880. It is
entitled “The Modifications Suffered
by Light in Passing Through a Very
Narrow Slit.”3 This report gives a
brief but accurate account of his obser-
vations on the already well known dif-
fraction phenomena produced by a
narrow slit. However, the subject
seems to have been new to Michelson,
and he reported his keen observations
on the color and polarization of the
light as he narrowed the slit width
while using sunlight for the source.
This early paper is certainly not one
of his major contributions, but it does
reveal his remarkable observational
ability as he describes precisely the
colors, polarization, and diffraction
patterns produced. This paper strong-
ly suggests he had already appreciated
that the key to meeting Maxwell’s
challenge for precision optics was es-
sentially to find a method of measure-
ment that would directly employ the
extremely short wavelengths of light
and not depend on the macroscopic
length and time measurements of ray
optics that he had employed exclusive-
ly in his earlier work.

When Michelson arrived at Helm-

Robert S. Shankland is Ambrose Swasey

Professor of Physics at Case Western Re-
serve University, Cleveland, Ohio.

Albert A. Michelson in 1927 at his desk in the Ryerson Physical Laboratory, University of
Chicago. This is one of two photographs, taken by H. P. Burch, that Michelson often said
he liked better than any others. (Courtesy of the Michelson M useum ) . Figure 1

38

HISTORY OF PHYSICS

The Michelson-Morley experiment as used in Cleveland in 1887, with its optical parts
mounted on a five-foot-square sandstone slab. This photograph was found in 1968 by D. T.
McAllister in a Michelson notebook at Mount Wilson Observatory. (Courtesy of the Michel-
son Museum and the Hale Observatories.) Figure 2

Holder for optical-flat “beam-splitter” of the

Michelson-Morley interferometer used in
1886-87 at what is now Case Western Re-
serve University. Figure 3

holtz’s laboratory in Berlin in the fall
of 1880, he experienced for the first
time the thrill of a well equipped and
active research center, for at that time
this was probably the outstanding lab-
oratory in Europe for physics research.
There also he was suddenly brought in
touch with the best apparatus avail-
able for experiments in optics, for
Helmholtz himself was already world
famous for his researches in physiologi-
cal optics. The questions that had
been raised in Michelson’s mind by the
phenomena of his narrow-slit experi-
ment in Washington had “sensitized”
him to react strongly and appreciate
fully the many new stimuli of Helm-
holtz’s laboratory. In any event, soon
after his arrival in Berlin his pondering
and search for an optical method that
would meet the severe requirements
posed by an ether-drift experiment
aroused his natural creative instincts
and he invented the Michelson inter-
ferometer. (But it is possible that he
had already conceived the essential el-
ements of the instrument while still in
Washington, where Newcomb had in-
troduced him to Alexander Graham
Bell who later, on Newcomb’s recom-
mendation, supplied the necessary
funds to have the first interferometer
built by Schmidt and Haensch in Ber-
lin.)

In later years he always stated that
the interferometer was devised specifi-
cally for the ether-drift experiment. It
is, of course, impossible to trace pre-
cise paths in the creative thinking of a
scientist and conclusively demonstrate
how he finally arrived at his goal, and
there are discontinuities in the process
that even the man, himself, cannot ex-
plain. But it seems clear that Max-
well’s letter and the narrow-slit experi-

ment in Washington were essential
spurs to Michelson’s genius for his in-
vention of the interferometer.

This instrument is a classic example
of symmetry, and apparent simplicity.
He dispensed with the narrow slits that
physicists had employed since the days
of Thomas Young to produce interfer-
ence between coherent light beams,
and instead used a large glass optical
flat silvered just enough on one face to
half reflect and half transmit the entire
wavefront of the light impinging on it,
thus giving much greater intensity and
permitting a wide range of experiments
that had been impossible with all ear-
lier optical apparatus. Once the two
coherent light beams were produced at
the optical “beam splitter,” they could
then each be directed by mirrors and
lenses in a variety of ways (through
moving water for example) and then be
reunited to add and subtract their vi-
brations to produce the beautiful pat-
terns of bright and dark interference
fringes that Michelson studied in one
experiment after another for the rest of
his life. He spent the last forty years
at the University of Chicago (figure 1 is
a photograph dating from this period).

Ether drift

We will note here only a few of the
great experiments he carried out with
his interferometer. As already stated,
it was specifically devised to measure
the motion of the Earth through the
ether, a medium that in those days was
universally believed to be essential for
the propagation of light. In this exper-
iment, first tried unsuccessfully at
Potsdam in 1881, and then after Mi-
chelson became the first professor of
physics at Case School of Applied
Science, it was conducted in its defini-

tive form (see figures 2 and 3) by Mi-
chelson and Morley at Cleveland in
1887.

One of the two coherent light beams
produced in the interferometer was
caused to traverse a to-and-fro path
along the direction of the Earth’s mo-
tion, while the other light beam trav-
elled along a path of exactly equal
length in a perpendicular direction.
On their return the two light beams
were recombined to produce white-
light interference fringes, so that the
central white fringe could serve as a
reference. Michelson had confidently
expected from calculations that, when
the apparatus was rotated so as to in-
terchange the positions of the two light
beams, the pattern of interference frin-
ges would shift and thus reveal the
Earth’s motion through the ether.
This procedure, in effect, compares
with great precision the speed of light
in the two arms of the interferometer.
The ether theory predicted that this
speed should be altered unequally by
the Earth’s motion, to a degree propor-
tional to the square of the ratio of the
Earth’s speed to that of light. The ap-
paratus was sensitive enough to have
shown this extremely small effect dis-
cussed by Maxwell, but no significant
shift of the interference fringes was ob-
served. The scientific world generally,
and Michelson in particular, were
greatly disappointed by this result,
which was in direct conflict with ac-
cepted theory at that time. It was
many years before the work of George
Fitzgerald, H. Antoon Lorentz, Jo-
seph Larmor, Henri Poincare and, fi-
nally, Albert Einstein carried theoreti-
cal physics to the point where Michel-
son and Morley’s result could not only
be explained, but served as an essen-

BEFORE OUR TIMES

39

tial basis for our modern concepts of
space and time.

It is a curious fact that for many
years Michelson seldom mentioned this
result. It did not appear in his Vice-
Presidential Address to the American
Association for the Advancement of
Science, delivered at Cleveland in
1888; his students at Case School of
Applied Science never heard of it in his
physics classes there, and it is absent
from his Nobel Prize lecture in 1907.
After many years Michelson did dis-
cuss it in his optics courses at the Uni-
versity of Chicago, but only after the
relativity theory was fully established;
even then it was described primarily in
its relation to the ether theory of Au-
gustin Fresnel and Lorentz, rather
than for its importance to relativity.4
But, in Einstein’s words, Michelson
had “led the physicists into new paths,
and through his marvelous experimen-
tal work paved the way for the devel-
opment of the theory of relativity. He
uncovered an insidious defect in the
aether theory of light as it then existed,
and stimulated the ideas of H. A. Lo-
rentz and Fitzgerald out of which the
special theory of relativity developed.
This in turn pointed the way to the
general theory of relativity, and to the
theory of gravitation.”5 As Robert A.
Millikan emphasized in 1948 at the
dedication of the Michelson Laboratory
in California, the ether-drift trial has
long been regarded as one of the two
greatest physics experiments per-
formed in the nineteenth century (the
other being the Faraday-Henry discov-
ery of electromagnetic induction).

Measuring the meter

But strangely enough this was not
the work for which Michelson was
awarded a Nobel Prize, the first such
award to an American. Rather, the
Prize was given primarily in recogni-
tion with Morley in Cleveland, and in
1887 they abruptly abandoned the
search for the ether to prove the feasi-
bility of their optical method for stan-
dardization of the meter.6 An early
form of interferometer built for this pur-
pose is now at Clark University and is
shown in figure 4 . Michelson alone com -
Paris which was jealously guarded
against damage or loss. Clearly a re-
producible standard of length was
highly desirable — one that could be
duplicated at any major laboratory in
the world.

The solution of the problem was first
undertaken by Michelson in collabora-
tion with Morley in Cleveland, and in
1887 they abruptly abandoned the
search for the ether to prove the feasi-
bility of their optical method for stan-
dardization of the meter.6 An early
form of interferometer built for this pur-
pose is now at Clark University and is
shown in figure 4. Michelson alone com-

Early interferometer of the type developed by Michelson and Edward W. Morley and used
by Michelson in Paris for measuring the standard meter in wavelengths of cadmium light,
1 892-93. (Courtesy of the Michelson Museum and Clark University. ) Figure 4

“Visibility curves” of interference fringes as a function of light-path differences in the two
interferometer arms (solid color curves on right), with the analyzed structure of the spec-
trum lines (colored peaks on left). Part a: Fine-structure doublet of H-alpha line of
hydrogen. Part b: Hyperfine structure in a line of thallium. Part c: The narrow red line
of cadmium used to standardize the meter. (From A. A. Michelson, “Light Waves and
Their Uses,” University of Chicago Press, 1 903.) Figure 5

40

HISTORY OF PHYSICS

Part of the system of evacuated pipes used in the Michelson-Gale-Pearson experiment at
Clearing, Illinois, 1924-25. This photograph shows, left to right; Charles Stein, Thomas J.
O'Donnell, Fred Pearson, Henry G. Gale, J. H. Purdy and an unidentified worker. (Courtesy
of the Michelson Museum and J. H. Purdy.) Figure 6

pleted the determination in Paris, and
since that time it has been a matter of
little concern whether or not the stan-
dard meter bar continues to exist, for
thanks to Michelson and the later de-
velopment of the orange-red line of
krypton7 as a new primary standard,
the length of a light wave is now the
official standard of length.

Two major discoveries were made by
Michelson and Morley in the course of
their standard meter work in Cleve-
land.8 To measure the meter in terms
of light waves it was essential that the
interference fringes in their special in-
terferometer should be produced by
light of an extremely narrow spectrum
line, so that interference between light
beams with a large difference in path
was possible. In the course of their
search for such a light source they ana-
lyzed many spectrum lines with the in-
terferometer by observing the changes
in the “visibility” of the fringes as the
path difference was increased. Today
this process is the basis of the large ac-
tivity in Fourier spectroscopy.9 They
were surprised to find that nearly all
spectrum lines are complex and thus
discovered what is now known as “fine-
structure” in the spectrum of hydro-
gen, and “hyperfine structure” in the
spectra of mercury and thallium (see
figure 5). It was many years before the
full significance of these findings for
atomic and nuclear physics was under-
stood, and it is interesting to note that
the detailed explanation of fine struc-
ture requires the relativity theory that
owed so much to Michelson’s other ex-
periments. The discovery of fine
structure and hyperfine structure will
always ensure their work an important
place among those experiments that
were basic for the development of
quantum mechanics and nuclear phys-
ics. They also were the stimuli that
led Michelson to his invention of the
echelon spectroscope, his harmonic an-
alyzer for more accurate Fourier spec-
troscopy, and his long program at the
University of Chicago in the ruling of
diffraction gratings.

The Earth’s rotation

Michelson’s experiments on the
ether continued from 1881 until 1929,
and “to the end he hoped to empirical-
ly prove there was this medium known
as the ether.”10 One of the most in-
teresting applications of his interfer-
ometer for this search was in the Mi-
chelson-Gale-Pearson experiment con-
ducted in 1924-25 on the Illinois Prai-
rie at what is now the Clearing indus-
trial area west of Chicago. As early as
1904 Michelson had proposed an inter-
ferometer experiment to reveal the
Earth’s rotation through the ether.
During 1921-23 he had made prelimi-
nary trials at the Mount Wilson Obser-
vatory, for after Eddington’s successful

solar-eclipse expeditions in 1919 had
found the deflection of starlight by the
sun, as predicted by general relativity,
there had been a great revival of inter-
est in all related experiments.

Michelson was in ill-health at the
time, but with the active collaboration
of Henry G. Gale, Fred Pearson and
Tom O’Donnell a large system of 12-
inch-diameter pipes for the light beams
was set up on a rectangle (300 meters
by 600 meters) on level ground. Figure
6 shows part of the large rectangle of
pipes employed. The two light beams
from a Michelson interferometer were
reflected, (one in each direction)
around the circuit of evacuated pipes.
The Earth’s rotation affected the
times of travel of the two beams un-
equally and thus would be revealed by
the interference fringes when the two
beams were re-united. A second sys-
tem of fringes from light-beams travel-
ling in a smaller rectangle of pipes es-
tablished the fiduciary point of the in-
terference pattern. Michelson’s poor
health and the excessive newspaper
publicity that attended this experi-
ment cooled his enthusiasm for the
work, but it was carried through suc-
cessfully. This experiment is the opti-
cal analogue of the Foucault pendu-
lum, and as such “only shows that the
Earth rotates on its axis,” as Michel-
son caustically remarked. The results
were definite, giving a shift of 0.25
fringe in the larger optical circuit.11
However, since this result was in
agreement not only with both the spe-
cial and the general theories of relativi-

ty but also with Fresnel’s old fixed-
ether theory, it did not give the deci-
sive test that had been hoped for.

The techniques of this experiment
were of great interest to Einstein, and
the following letter from him accurate-
ly describes its relation to relativity:

September 17, 1953
Dear Dr. Shankland:

The Michelson-Gale experiment
does, of course, concern the relativity
question but, as you mentioned
yourself, not insofar as relativity
theory differs from Lorentz’ theory
based on an ether at rest. My admi-
ration for Michelson’s experiment is
for the ingenious method to compare
the location of the interference pat-
tern with the location of the image of
the light source. In this way he ov-
ercomes the difficulty that we are
not able to change the direction of
the earth’s rotation.

Sincerely yours,

Albert Einstein (signed)

However, modern applications of this
method in the ring-laser gyro have
proved to be of great value for measur-
ing and guiding rotations in the navi-
gation of satellites, missiles, and air-
craft.

The diameter of a star

One final application of the interfer-
ometer should be emphasized — in this
case to astronomy. As shown in figure
7, Michelson adapted his instrument
for use with large telescopes to mea-

BEFORE OUR TIMES

41

until the end of his days (1931). 14 The
accuracy of his results improved stead-
ily over the years and the continuing
importance of this fundamental con-
stant for science has fully justified the
care that he lavished on its determina-
tion.

* * *

This article has been adapted from an ad-
dress given 21 October 1973 at the New York
University Hall of Fame Meeting at Town
Hall, New York City.

References

Michelson's twenty-foot stellar interferometer mounted on top of the 100-inch Hooker
telescope at Mount Wilson Observatory in 1920, as used to measure the angular diameter
of Betelgeuse. The outer two (movable) mirrors collect the starlight and the two inner
ones direct it to the eyepiece. (Courtesy of the Hale Observatories.) Figure 7

sure the diameters of heavenly bodies.
First, at the Lick Observatory in 1891,
he determined the sizes of Jupiter’s
satellites;12 later, in 1920 at the Mount
Wilson Observatory, Michelson and
Pease measured for the first time in
history the angular diameter (0.047
seconds of arc) of a star (Betelgeuse).13
This latter feat was one of the greatest
triumphs of his life-long devotion to
precision measurements with light
waves, and extensions of his method
are now an essential element for much
work in long baseline radioastronomy.
After explaining the technical details
of the stellar measurement to a joint

meeting of the American Physical So-
ciety and the AAAS, he then urged his
children “to always remember the
wonder of it.”

In closing this account we should
also realize that Michelson’s other con-
tinuing scientific interest in addition to
his interferometer was the measure-
ment of the speed of light. He pur-
sued this for over half a century from
his first determination along the old
sea-wall at Annapolis (1877-79), then
across the Potomac in Washington,
then along the railroad tracks in Cleve-
land (1882-84) and, finally, at Mount
Wilson and at Santa Ana in California

1. A. Ganot, Treatise on Physics, (Atkin-
son’s translation), New York (1873).

2. J. C. Maxwell, reprinted in Nature 21,
314 (1880).

3. A. A. Michelson, Smithsonian Misc.
Collections 20, 119 and 148 (1881).

4. V. O. Knudsen, Notes of Michelson’s
University of Chicago Lectures made in
1917. Also correspondence with Michel-
son’s students, Harvey Fletcher, Ralph
D. Bennett and Richard L. Doan.

5. A. Einstein, Science 73, 379 (1931).

6. A. A. Michelson, E. W. Morley, Amer. J.
Sci.34, 427 (1887).

7. Natl. Bur. of Std. Publ. 232, April 1961.

8. A. A. Michelson, E. W. Morley, Amer. J.
Sci.38, 181 (1889).

9. J. N. Howard, G. A. Vanasse, A. T.
Stair, D. J. Baker, Aspen Conference on
Fourier Spectroscopy, 1970.

10. Letter of T. J. O’Donnell (Michelson’s
instrument maker) to R. S. Shankland,
12 July 1973.

11. A. A. Michelson, H. G. Gale, F. Pear-
son, Astrophys. J. 61, 137 (1925).

12. A. A. Michelson, Publ. Astron. Soc. Pa-
cific 3, 274(1891).

13. A. A. Michelson, F. G. Pease, Astro-
phys. J. 53, 249 (1921).

14. Dorothy Michelson Livingston, The

Master of Light, Scribners, New York
(1973). □

Poincare and cosmic evolution

Among his other, better known, studies this nineteenth-century
“mathematical naturalist’’ enquired into the origin and stability of the solar
system, the fate of the universe and the shapes of rotating fluid masses.

Stephen G. Brush

PHYSICS TODAY / MARCH 1980

Henri Poincare is well known today for his
contributions to many areas of mathe-
matics and his popular writings on
science. His attempts to apply physical
theories to the evolution of the solar sys-
tem and the rest of the universe are
largely forgotten, except by a few spe-
cialists. Yet the crisp lucid prose of this
brilliant thinker1 can still help the mod-
ern reader to appreciate the worldview of
nineteenth-century science, and provides
a useful introduction to a fascinating
historical phenomenon that I will call “the
mathematician as naturalist” (see the box
on page 44).

Many of Poincare's colleagues, I sup-
pose, silently waved the flag of caution
when he published his ideas on cosmic
evolution. Speculations about the re-
mote past and the distant future of the
world should be avoided by a sensible
mathematician, especially at a time when
scientists are no longer confident that
their fundamental theories are valid even

for phenomena that can be studied in the
laboratory. It is obviously dangerous to
extrapolate those theories to the indefi-
nitely large domains of space and time
variables needed to explain such hypo-
thetical events as the origin of the solar
system, the birth of the Moon, the long-
term periodicity of planetary orbits, the
attrition of the Earth’s rotation, and the
ultimate fate of the entire universe. In
France, where the positivist influence was
still strong at the end of the century, sci-
entists were discouraged from theorizing
about the nature of the world beyond
their immediate observations.

Yet the temptation to study cosmic
evolution, already irresistible for anyone
with a modicum of curiosity about the
world, is strengthened for a mathemati-
cian by the knowledge that refined rea-
soning and careful calculation have in the
past produced some remarkable advances
in physical astronomy. Beyond the ob-
vious example of Isaac Newton, one re-

calls several successful applications of
mathematics; three of the most spectac-
ular happen to have been made by
Frenchmen. In 1758 Alexis Clairaut
predicted the return of Halley’s comet,
expected the following year, within 30
days, by taking account of the effect of the
major planets on its orbit. In 1784 Pierre
Laplace showed that the “long inequality”
of Jupiter and Saturn was cyclic, not
secular, thus eliminating one of the major
reasons for doubting the stability of the
solar system. In 1846 Urbain LeVerrier
pinpointed the position of a previously
unknown planet by analyzing anomalies
in the orbit of Uranus, and the resulting
discovery of Neptune demonstrated again
the amazing power of Newtonian celestial
mechanics.

As its hegemony crumbled in theoreti-
cal physics and other scientific disciplines
during the 19th century, France retained
its leadership (though certainly not a
monopoly) in mathematical astronomy.

AIP NIELS BOHR LIBRARY

BEFORE OUR TIMES

43

Poincare, heir to this glorious tradition,
could hardly ignore the classic problems
that had elicited brilliant contributions
but not definitive solutions from his pre-
decessors; surely he could peer a little
further by standing on the shoulders of
those giants.

The problems, in order of Poincare’s
most intense concern with them, were:

► equilibrium figures of rotating fluid
masses (1885)

► stability of the solar system and ulti-
mate fate of the universe (1889)

► origin of the solar system (191 1).
These problems were of course closely
interrelated; in particular, we will have to
discuss aspects of Laplace’s nebular hy-
pothesis in connection with each of
them.

Rotating fluids

The first problem goes back to Newton
and Christiaan Huygens, who concluded
that the centrifugal force associated with
the Earth’s rotation would cause it to
bulge at the equator and flatten at the
poles, taking the form of an oblate
spheroid. Because two leading astrono-
mers in Paris — Jean-Dominique Cassini
and his son Jacques — and some theorists
following the ideas of Rene Descartes
came to the opposite conclusion, this
problem was seen as a crucial test of the
competing Newtonian and Cartesian
systems of the world. The results of
French expeditions, in the 1730’s, to
measure the length of the degree of lati-
tude at high and low latitudes, confirmed
the predicted flattening at the poles and
thus helped to ensure the victory of
Newton over Descartes.2

To calculate the precise geometrical
form of the rotating fluid, including the
quantitative relation between speed of
rotation and deviation from sphericity,
proved to be a much more difficult task,
but the work was motivated by its geo-
physical significance. It was generally
believed that the Earth had been formed
as a hot fluid, which cooled, solidified (at
least on the outside), and contracted. By
conservation of angular momentum,
contraction would increase the speed of
rotation and hence the amount of equa-
torial bulge. Is the present oblateness
just what one would expect for a fluid
mass spinning at the present rotation
speed of the Earth? If not, does it indi-
cate that the Earth solidified while spin-
ning faster or more slowly than it does
now? A secular decrease in rotation rate
might be attributable to dissipation by
tidal friction, and would presumably be
associated with transfer of angular mo-
mentum to the Moon.

Stephen G. Brush is a professor in the Depart-
ment of History and the Institute for Physical
Science and Technology, and a member of the
Committee on History and Philosophy of
Science, at the University of Maryland, College
Park.

A possible objection to the hypothesis
of a frozen-in equilibrium shape would be
that a solid sphere the size of the Earth,
composed of known materials such as
rocks and iron, would lack the mechanical
strength to maintain a non-equilibrium
shape against distorting forces, and hence
must have very nearly the same shape as
a fluid mass rotating at the present rate.

The early history of this problem has
bpen discussed in excruciating detail by
Isaac Todhunter.2 I will mention only
the bare minimum needed to put Poin-
care’s work in context.

Ellipsoids

In 1742 Colin Maclaurin showed that a
series of ellipsoids of revolution would be
equilibrium figures for low rates of rota-
tion. There was considerable further work
by Laplace and others on the details of the
solution. It was usually assumed, in
mathematical treatments, that the fluid
is ideal (no viscosity), homogeneous, and
incompressible, conditions that are ob-
viously not satisfied inside the Earth; yet
it was apparently thought that if the
problem could be solved for a more real-
istic model, only minor qualitative cor-
rections would be obtained.

In 1834, C. G. J. Jacobi opened up a new
aspect of the subject by showing that an
ellipsoid with three unequal axes can be
a figure of equilibrium. The possibility
that a rotating fluid does not have com-
plete rotational symmetry was apparently
a shock to the intuition of some 19th-
century scientists. The Jacobi ellipsoid
was proposed as a model for variable stars,
on the assumption that the asymmetrical
bulges would emit more light than the
flattened sides and thus rotation would
produce an apparent change in bright-
ness.

Poincare’s interest in the problem was
stimulated by a section in the Treatise on
Natural Philosophy by William Thom-
son and P. G. Tait; moreover, he had been
teaching fluid mechanics at the Sorbonne
starting in 1881, and was dissatisfied with
the standard textbook treatments of ro-
tating fluids.3 His first papers do no
more than supply explicit proofs of
statements made by Thomson and Tait
concerning the stability of annular sur-
faces of revolution. That problem is
closely related to the question of the
physical state of Saturn’s rings, and this
connection may explain how he came
across Sonya Kovalevsky’s memoir on
Saturn's rings; he subsequently credited
her with introducing the appropriate
methods for such problems.

In his long memoir of 1885, Poincare
discussed a new series of equilibrium fig-
ures that branch off from the Jacobi el-
lipsoids with increasing angular momen-
tum, just as the Jacobi ellipsoids branch
off from the Maclaurin ellipsoids. The
new figures were later called piriform
(pearshaped); they can be described
qualitatively by imagining an ellipsoid cut

in half, then letting one half flatten and
approach a hemisphere while the other
becomes more and more elongated. (See
figures on pages 46 and 47.) A furrow
develops around the elongated part,
giving the impression that it is being
“strangled” or “wants to separate” into a
small and large part. Poincare apologizes
for using such non-mathematical lan-
guage and cautiously points out that it is
difficult to say whether this separation
will indeed take place. Nevertheless he
thinks it is possible that the next stage of
evolution of the system will be a stable
equilibrium state of a large and a small
body revolving around each other, com-
parable to a planet and a satellite. He
notes (as he did on several other occa-
sions) that this process is not necessarily
the one envisaged in Laplace’s theory of
the origin of the solar system, since ac-
cording to that theory the primeval neb-
ula is very strongly concentrated at the
center, whereas the fluid masses consid-
ered by Maclaurin, Jacobi and Poincare
have uniform density.

Poincare’s 1885 paper “came as a rev-
elation” to George Howard Darwin (son
of Charles Robert Darwin). Darwin re-
called, in awarding the Gold Medal of the
Royal Astronomical Society to Poincare
in 1900, 4

I had attempted to attack the ques-
tion from the other end, and to trace
the coalescence of two detached bod-
ies into a single one — but alas! I have
to admit that my work contained no
far-reaching general principles — no
light on the stability of the systems I
tried to draw— nothing of all that
which renders Poincare’s memoir one
that will always mark an important
epoch in the history not only of evolu-
tionary astronomy, but of the wider
fields of general dynamics.

In 1878 Darwin had traced the history of
the Earth-Moon system, as influenced by
tidal forces, back to a time, 54 million
years ago, when the Moon was only 6000
miles from the surface of the Earth, and
its time of revolution around the Earth
was the same as the Earth’s rotation pe-
riod at that epoch, 5 hours 36 minutes.
These results point strongly to the
conclusion that, if the moon and earth
were ever molten viscous masses, then
they once formed parts of a common
mass.

We are thus led at once to the in-
quiry as to how and why the planet
broke up. The conditions of stability
of rotating masses of fluid are unfor-
tunately unknown, and it is therefore
impossible to do more than speculate
on the subject.5

Since Poincare, apparently uncon-
cerned about the passage of time on a
small scale, did not date his letters to G.
H. Darwin, I cannot say just when their
collaboration began, but it was in full
swing by 1901. In that year each pre-
sented a long memoir to the Royal Society

44

HISTORY OF PHYSICS

of London on pear-shaped figures.
Poincare thought these figures are prob-
ably stable, but this could be proved only
by very complicated calculations, which
he hoped to facilitate by reducing the
stability condition to a convenient ana-
lytical form. Darwin performed the ac-
tual calculations for Poincare’s theory,
and concluded that the pear-shaped fig-
ures are indeed stable. This would imply
that as the fluid planet cools and con-
tracts, a part of it gradually separates but
remains in an orbit close to the primary
body. The other alternative, if the
pear-shaped figure is never stable, is that
the body suddenly undergoes an enor-
mous deformation and a series of oscilla-
tions, followed by catastrophic disinte-
gration.

Darwin’s conclusion was contradicted
in 1905 by the Russian mathematician
Alesksandr Mikhailovich Lyapunov, who
determined by a different method that
the pear-shaped figure is initially unsta-
ble. The disagreement was still unre-
solved at the time of Poincare’s death; he
was more inclined to believe Lyapunov,
having earlier been impressed by his in-
cisive work on similar problems.

In 1915 James Jeans tackled the prob-
lem by another method, which enabled
him to discover an error in Darwin’s cal-
culations; he then confirmed Lyapunov’s
conclusion that the pear-shaped figures
are always unstable. An even stronger
result in the same direction was obtained
by Elie Cartan in 1924. “And at this
point,” the astrophysicist S. Chandrase-
khar noted, “the subject quietly went into
a coma.” 6

Chandrasekhar speaks rather harshly
of Poincare’s influence on this field of
research. He says Poincare’s “spectacu-
lar discovery” of the pear-shaped figures
“channeled all subsequent investigations
along directions which appeared rich with
possibilities; but the long quest it entailed
turned out, in the end, to be after a chi-
mera. . . . The grand mental panorama
that was thus created was so intoxicating
that those who followed Poincare were not
to recover from its pursuit.” 7

Poincare’s pear-shaped figures are no
longer believed to play any role in cosmic
evolution. But the hypothesis that fis-
sion following rotational instability of a
fluid mass could lead to the formation of
double-star systems is still being investi-
gated by at least a few astrophysicists; so
Poincare’s general approach may come
back into favor.8

Stability of the solar system

Poincare’s concern with “stability”
showed up in another mathematical
problem with greater relevance to as-
tronomy than the evolution of homoge-
neous fluid masses: the effect of gravi-
tational perturbations on the orbits of
planets in the solar system. In its sim-
plest form this is the famous “three-body
problem.” Whereas a single planet could

The “mathematical naturalist”

William Thomson (1824-1907), who became
Lord Kelvin in 1892, was the most respected
British scientist of his day. Among his many
interests was the application of mathemati-
cal and physical principles to the study of the
Earth and solar system. What label should
be used to describe such a person? Here
is his own proposal (1862):

“ ‘Naturalist. A person well versed in
Natural Philosophy.' — Johnson's Dictionary.
Armed with this authority, chemists, elec-
tricians, astronomers and mathematicians
may surely claim to be admitted along with
merely descriptive investigators of nature to
the honourable and convenient title of Nat-
uralist, and refuse to accept so un-English,
unpleasing, and meaningless a variation from
old usage as 'physicist.' “

(Mathematical and Physical Papers, Cam-
bridge University Press, Cambridge
(1882-1911), Volume 3, page 318.)

continue to move forever in a Kepler orbit
around the Sun in the absence of fric-
tional resistance and other forces, the
presence of a second planet must disturb
its motion and, over a sufficiently long
period of time, might cause it either to
spiral into the Sun or wander off to in-
finity.

According to the “clockwork universe”
concept, or the “Newtonian world ma-
chine” as it is sometimes called by histo-
rians of ideas, the effect of perturbations
is cyclic rather than secular: each planet
remains in an orbit whose dimensions
change back and forth between fixed
limits. According to Newton himself, if
nothing more than gravitational forces
were involved, the perturbations would
have a secular effect and occasional (di-
vine?) intervention is needed to restore
the system to its proper state. That
statement was the occasion for the Leib-
niz-Clarke debate of 1715-16, in which
Gottfried Wilhelm Leibniz accused
Newton of disrespect for God through the
implication that He was not competent
enough to construct a clockwork universe
that could run forever by itself, but rather
has to wind it up from time to time.
Newton stood his ground, arguing that to
relegate God’s actions to the indefinite
past was the first step toward eliminating
Him entirely from our conception of the
world.

During the 18th century, research in
celestial mechanics focused on three “in-
equalities,” meaning, in this context, de-
viations from cyclic motion in Kepler or-
bits. Each inequality appeared to be a
secular effect of the kind mentioned by
Newton, and thus to endanger the long-
term stability of the solar system:

► The secular acceleration of the Moon,
noticed by Edmund Halley in 1693 and
apparently confirmed by the detailed

THOMSON

calculations of Tobias Mayer, implied
that the Earth-Moon distance was de-
creasing; if it continued, the Moon would
eventually crash into the Earth.

► The long inequality of Jupiter and
Saturn, also first noted by Halley (1695),
was a gradual acceleration of Jupiter and
a retardation of Saturn. The ultimate
result would be the loss of Saturn — one of
the most interesting heavenly bodies,
because of its rings — from the solar sys-
tem, and gradual destruction of the inner
planets as Jupiter fell toward the Sun.

► The decrease in the obliquity of the
ecliptic, from about 23°5T in the 3rd
century BC to about 23°28' in the 18th
century AD, threatened to abolish sea-
sonal variations of climate on Earth, if it
led to a final state in which the Earth’s
axis of rotation is always parallel to the
axis of its orbit around the Sun.

Following heroic but inconclusive work
on these problems by Leonhard Euler and
Joseph Lagrange, Laplace finally ex-
plained all three phenomena as cyclic
rather than secular effects, and moreover
proved some general theorems suggesting
that the parameters of planetary orbits
oscillate around fixed values. Thus by
the standards of 18th-century celestial
mechanics Laplace proved the stability of
the solar system, and justified the clock-
work universe philosophy. This is why he
might have replied, when Napoleon pro-
tested that his book on the universe failed
to mention its creator, “Sir, I have no need
of that hypothesis.” (So Newton was
right when he warned that the clockwork
view would lead scientists to atheism; yet
his own theory of gravity started them on
that path!)

This digression on 18th-century celes-
tial mechanics may suggest why Laplace
had such a high reputation in the 19th
century — a reputation that 20th-century

BEFORE OUR TIMES

45

scientists may find hard to appreciate
because the three inequalities mentioned
above, and the other problems he solved
such as the speed of sound, are familiar
only to a few specialists. Moreover, we
now know that his analysis of the first
inequality was defective— the Moon is
slowing down, not speeding up, so that it
was much closer to the Earth in the past;
hence the possibility of explaining its or-
igin in the way G. H. Darwin sug-
gested— and that his arguments for the
stability of the solar system are not con-
clusive. But in the 19th century Lapla-
ce’s authority in astronomy was so great
that his nebular hypothesis for the origin
of the solar system was widely accepted in
spite of many serious defects and Lapla-
ce’s own diffidence in presenting it.

Evolutionary philosophies

In a way it was Laplace who furnished
the physical basis for the evolutionary
philosophy that dominated science in the
late 19th century. This came about by
two rather different routes. First, the
supposed proof of the stability of the solar
system implied that the Earth had re-
mained at more or less the same average
distance from the Sun for an indefinitely
long time in the past; hence the temper-
ature at the surface of the Earth had been
roughly the same for countless millions of
years. Therefore geologists (Hutton,
Playfair, Lyell) could assume that the
same physical causes that we now see in
action had been operating with the same
intensity in the past, favoring a “unifor-
mitarian” as opposed to a “catastrophist”
approach in geological explanation.
Charles Darwin was then able to invoke a
geological time-scale on the order of
hundreds of millions of years to permit a
slow process of biological evolution by
natural selection.

Second, the nebular hypothesis pro-
vided an example of evolution in the
universe, which could be taken (as it was,
for example, by Robert Chambers and
Herbert Spencer) as the first stage of a
comprehensive scheme of cosmic evolu-
tion leading to the emergence of plants,
animals and humans. In fact, the nebular
hypothesis was attacked on theological
grounds (Laplace’s reputation as an ath-
eist may have played some part in this)
just as biological evolutionary theories
were castigated. The success of Laplace’s
supporters in overcoming this criticism,
and the fact that intellectuals thereby
became accustomed to talking about ev-
olution in the cosmos, may have assisted
the favorable reception of Charles Dar-
win’s theory.9

Nevertheless there was a conflict be-
tween these two kinds of evolution, for the
nebular hypothesis implied that the Earth
had originally been a hot fluid mass that
subsequently solidified and cooled. The
time needed to cool to the present state
could be estimated from Fourier’s heat-
conduction theory (assuming no present

sources of heat inside the Earth) and the
resulting “age” of the Earth was much less
than the time geologists needed for their
uniformitarian explanations. It was also
much less than the time Darwin had sug-
gested was available for biological evolu-
tion; hence arose the famous controversy
on the age of the Earth. It was settled by
the discovery of radium. Though
Thomson’s estimate of the age of the
Earth turned out to be much too low, this
problem did play an important role in the
origin of his 1852 principle of the dissi-
pation of energy.10

Thermodynamics and stability

When Poincare became interested in
the stability of the solar system in the
1880’s, the problem had acquired physical
as well as mathematical aspects. Ac-
cording to Thomson’s dissipation princi-
ple, or the generalized second law of
thermodynamics, irreversible processes
in the solar system should push it toward
a final equilibrium state, in which plane-
tary and satellite orbits would not neces-
sarily be the same as they are now. On
the other hand the work of Rudolf
Clausius, James Clerk Maxwell and
Ludwig Boltzmann suggested that irre-
versible processes themselves might be
explained in terms of the motions and
collisions of molecules obeying Newton’s
laws. Irreversibility might be no more
than a statistical effect resulting from our
inability to keep track of the paths of the
immense number of molecules in a mac-
roscopic sample, as the counterexample
of Maxwell’s Demon suggested.

Poincare’s memoir on the stability of
the solar system, or rather on the three-
body problem and the equations of dy-
namics, was submitted in 1889 for a prize
offered by King Oscar II of Sweden. His
motivation was at first primarily mathe-
matical— the problem involved the
properties of solutions of differential
equations near singularities — but by the
time he had won the prize and published
the memoir (1889) he had acquainted
himself with the physical as well as the
astronomical aspects of the problem. As
in the case of rotating fluids, he ac-
knowledged his debt to the results of “la
savante mathematicienne” Sonya Kova-
levski.

Stability, Poincare points out, may
have two different meanings in celestial
mechanics. It may entail that the point
P representing the position of the system
in space (in general, in the n -dimensional
phase space of positions and momenta),
never goes beyond a fixed distance from
its starting point. Alternatively, one may
define “stability in the sense of Poisson”
as the condition that P returns after a
sufficiently long time as close as one likes
to its original position. Poincare’s re-
currence theorem states that almost all
solutions of the equations of mechanics
possess stability in the sense of Poisson,
provided that P never leaves a fixed vol-

ume V. In general the system will return
not once but infinitely many times to a
configuration very close to its initial
one.11

The claim that “almost all” solutions
are stable is expressed by Poincare as
follows: there are an infinite number of
unstable solutions, as well as an infinite
number of stable solutions, but the for-
mer are the exception and the latter the
rule — in the same sense that the rational
numbers are exceptions while the irra-
tionals are the rule. The probability that
the initial conditions in any real problem
correspond to an unstable solution is
zero.

The historian of mathematics would
presumably want to investigate the extent
to which Poincare was familiar with the
work of Georg Cantor, Emile Borel, and
Henri Lebesgue, and how much that work
may have influenced his conception of the
recurrence theorem in 1889 and later. I
cannot go into this point here except to
note that there is a brief remark in the
1889 paper to the effect that Cantor has
shown that a set can be “perfect” but not
“continuous”; hence one cannot, strictly
speaking, draw conclusions about the in-
finity of trajectories near periodic solu-
tions. It was my feeling, when I first
wrote on Poincare’s recurrence theorem
several years ago, that his proof would not
be considered rigorous by a 20th-century
mathematician because it lacked the no-
tion of a set of measure zero, and indeed
that was the view of Constantin Car-
atheodory who provided a measure-the-
oretical proof in 1919. However, Clifford
Truesdell tells me that there is nothing
really wrong with Poincare’s proof; the
measure-theoretical reformulation by
Caratheodory is merely cosmetic.

From my viewpoint one of the most
interesting of all of Poincare’s writings is
a short paper, “Le mecanisme et l’exper-
ience,” which he published in Revue de
Metaphysique et de Morale in 1893.
Here he alludes to the contemporary crisis
of the atomistic philosophy in physical
science, and discusses the cosmological
implications of his recurrence theorem.
First he describes the “reversibility par-
adox” that arises when one tries to rec-
oncile the Second Law of Thermody-
namics with any theory based on Newto-
nian mechanics. The fundamental
equation of Newtonian mechanics, F =
ma, is time reversible, and therefore any
motion in one direction in time can be
replaced by a motion in the opposite di-
rection without violating Newton’s
laws — the entire system can run either
“backwards” or “forwards.” Yet all ex-
perience teaches that natural phenomena
are irreversible. The “English kinetic
theorists” (a curious omission of
Boltzmann!) have made a valiant attempt
to overcome this difficulty, through a
statistical explanation — “the apparent
irreversibility of natural phenomena is . . .
due to the fact that the molecules are too

46

HISTORY OF PHYSICS

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i*

ft /ft /e

>

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JU Cite ft* *<- t’-Ab*~*c cte f ctfyt /of cicc y*f t* •}*./* «•/.,. <*

Poincare’s pear-shaped figure of equilibrium is postulated in an 1885 memoir, illustrated in this
handwritten version in the Ouvres (ref. 1, vol. XI, page 283). The shaded areas in the sketch indicate
those parts of the surface that lie within the ellipsoid Poincare has drawn with a dashed line.

small and too numerous for our gross
senses to deal with them.” 12 Maxwell’s
example of the fictional demon shows how
the Second Law could be violated if this
were not the case.

Poincare then introduces his own con-
tribution to the debate:13

A theorem, easy to prove, tells us
that a bounded world, governed only
by the laws of mechanics, will always
pass through a state very close to its
initial state. On the other hand, ac-
cording to accepted experimental laws
(if one attributes absolute validity to
them, and if one is willing to press
their consequences to the extreme),
the universe tends toward a certain
final state, from which it will never
depart. In this final state, which will
be a kind of death, all bodies will be at
rest at the same temperature.

I do not know if it has been re-
marked that the English kinetic theo-
ries can extricate themselves from this
contradiction. The world, according
to them, tends at first toward a state
where it remains for a long time with-
out apparent change; and this is con-
sistent with experience; but it does
not remain that way forever, if the
theorem cited above is not violated; it
merely stays there for an enormously
long time, a time which is longer the
more numerous are the molecules.
This state will not be the final death
of the universe, but a sort of slumber,
from which it will awake after millions
of millions of centuries.

According to this theory, to see heat
pass from a cold body to a warm one,
it will not be necessary to have the
acute vision, the intelligence, and the
dexterity of Maxwell’s demon; it will
suffice to have a little patience.

In 1896 the mathematician Ernst Zer-
melo used Poincare’s recurrence theorem
to attack the atomistic theory of heat and
the mechanical worldview in general. He
had not seen Poincare’s 1893 paper
quoted above — he says that Poincare had
not noticed the applicability of his own
theorem to the mechanical theory of
heat — and that paper seems to have been
missed by all the other participants in the
debate about the “recurrence paradox.”
Zermelo’s position is that the Second Law
does have absolute validity, and therefore
entropy can never decrease. According
to the mechanical theory of heat a physi-
cal system is represented by a collection
of atoms obeying Newtonian mechanics;
it must obey the recurrence theorem and
therefore its entropy will eventually de-
crease in order to return to its initial
value. The only acceptable way to avoid
the contradiction is to abandon the me-
chanical theory.

Boltzmann, the major defender of the
mechanical theory at this time, conceded
that Poincare’s recurrence theorem is
valid; moreover, he claimed that it is
completely in harmony with his own sta-

tistical viewpoint, which leads one to ex-
pect that there is a small but finite prob-
ability that the system will be in any
possible state, including the initial
one — hence it will eventually reach that
state if you wait long enough. But he re-
jected Zermelo’s assertion that there is a
contradiction between recurrence and the
Second Law; the time for the predicted
return to the initial state is many orders
of magnitude greater than the times for
which the Second Law has been veri-
fied.14

Poincare did not comment on
Boltzmann’s statistical interpretation of
the Second Law until a few years later,
but in a popular article on the stability of
the solar system (1898) he stated that
entropy always increases. When it has
once changed from its original value, “it
can never return again . . . The world
consequently could never return to its
original state, or to a slightly different
state, so soon as its entropy has changed.
It is the contrary of stability.” 15

Poincare clearly regards the periodic
solutions demanded by his recurrence
theorem as artefacts of the mathematical
idealization employed in treating the solar
system as a collection of mass points
moving in a vacuum, interacting only with

an inverse-square attractive force. But
the problem of the stability of the solar
system is different from that of solving the
set of equations usually considered by
mathematicians:

Real bodies are not material points,
and they are subject to other forces
than the Newtonian attraction.
These complementary forces ought to
have the effect of gradually modifying
the orbits, even when the fictitious
bodies, considered by the mathemati-
cian, possess absolute stability.

What we must ask ourselves then is,
whether this stability will be more
easily destroyed by the simple action
of Newtonian attraction or by these
complementary forces.

When the approximation shall be
pushed so far that we are certain that
the very slow variations, which the
Newtonian attraction imposes on the
orbits of the fictitious bodies, can only
be very small during the time that suf-
fices for the complementary forces to
destroy the system; when, I say, the
approximation shall be pushed as far
as that, it will be useless to go further,
at least from the point of view of ap-
plication, and we must consider our-
selves satisfied.

BEFORE OUR TIMES

47

But it seems that this point is at-
tained; without quoting figures, I
think that the effects of these comple-
mentary forces are much greater than
those of the terms neglected by the
analysts in the most recent demon-
strations on stability.

Let us see which are the most im-
portant of these complementary forc-
es. The first idea which comes to
mind is that Newton’s law is, doubt-
less, not absolutely correct; that the
attraction is not rigorously propor-
tional to the inverse square of the dis-
tances, but to some other function of
them. In this way Prof. Newcomb
has recently tried to explain the
movement of the perihelion of Mercu-
ry. But it is soon seen that this would
not influence the stability . . .

The Second Law of Thermodynamics
does, however, destroy the stability of any
real physical system, through the action
of irreversible processes. In particular:

► The existence of a resisting medium in
interplanetary space seems to be indi-
cated by anomalies in the motion of
Encke’s comet. This would eventually
cause the planets to fall into the Sun; but
the estimated effect is very small.

► Tidal forces acting on deformable

bodies (liquid or solid) dissipate energy at
a significant rate. As Charles-Eugene
Delaunay and G. H. Darwin have shown,
the effect of these forces has been to slow
the rotation of the Earth, and to force the
Moon to keep the same face toward the
Earth. In the future, the rotation of the
Earth will also become synchronous with
the motion of the Moon around it, and the
orbit of the Moon will become precisely
circular. Both the month and the day will
become equal to about 65 of our present
days.

Such would be the final state if
there were no resisting medium, and if
the earth and the moon existed alone.

But the sun also produces tides, the
attraction of the planets likewise pro-
duces them on the sun. The solar sys-
tem therefore would tend to a condi-
tion in which the sun, all the planets
and their satellites, would move with
the same velocity round the same axis,
as if they were parts of one solid in-
variable body. The final angular ve-
locity would, on the other hand, differ
little from the velocity of revolution of
Jupiter. This would be the final state
of the solar system if there were not a
resisting medium; but the action of
this medium, if it exists, would not

allow such a condition to be assumed,
and would end by precipitating all the
planets into the sun . . .

This is not all: the earth is magnet-
ic, and very probably the other plan-
ets and the sun are the same. The fol-
lowing well-known experiment is one
which we owe to Foucault: a copper
disc rotating in the presence of an
electromagnet suffers a great resis-
tance, and becomes heated when the
electromagnet is brought into action.
A moving conductor in a magnetic
field is traversed by induction cur-
rents which heat it; the produced heat
can only be derived from the vis viva
of the conductor. We can therefore
foresee that the electrodynamic ac-
tions of the electromagnet on the cur-
rents of induction must oppose the
movement of the conductor. In this
way Foucault’s experiment is ex-
plained. The celestial bodies must
undergo an analogous resistance be-
cause they are magnetic and conduc-
tors.

The same phenomenon, though
much weakened by the distance, will
therefore be produced; but the effects,
being produced always in the same di-
rection, will end by accumulating;
they add themselves, besides, to those
of the tides, and tend to bring the sys-
tem to the same final state.

Thus the celestial bodies do not es-
cape Carnot’s law, according to which
the world tends to a state of final rep-
ose. They would not escape it, even if
they were separated by an absolute
vacuum. Their energy is dissipated;
and although this dissipation only
takes place extremely slowly, it is suf-
ficiently rapid that one need not con-
sider terms neglected in the actual
demonstrations of the stability of the
solar system.

Poincare’s confidence in the absolute
validity of the Second Law survived the
efforts of Maxwell, Boltzmann, and J. W.
Gibbs to establish a statistical interpre-
tation, but finally succumbed to a much
less sophisticated argument. In 1904 he
announced to the Congress of Arts and
Sciences at St. Louis that the phenome-
non of Brownian movement is a visible
violation of the Second Law, as Leon
Gouy had suggested fifteen years ear-
lier:16

... we see under our eyes now motion
transformed into heat by friction, now
heat changed inversely into motion,
and that without loss since the move-
ment lasts forever. This is the con-
trary of the principle of Carnot.

If this be so, to see the world return
backward, we no longer have need of
the infinitely subtle eye of Maxwell’s
demon; our microscope suffices us.
Gouy’s suggestion had been generally ig
nored by physicists, and it was not until
a year after Poincare’s St. Louis ad-
dress, when Albert Einstein published a

48

HISTORY OF PHYSICS

quantitative theory of Brownian motion,
that the integrity of the Second Law was
seriously compromised. After the ex-
perimental confirmation of Einstein’s
theory by Jean Perrin, scientists could no
longer doubt the essential truth of
the Maxwell-Boltzmann statistical
theory — or for that matter the existence
of atoms.17

But can the Second Law really be re-
versed on the astronomical scale? Can
the heat death of the universe be avoided?
Poincare’s last pronouncement on this
subject was elicited by a new cosmological
hypothesis, developed beginning in 1903
by the Swedish physical chemist Svante
Arrhenius. According to Arrhenius, the
universe is like a giant heat engine, oper-
ating by heat flow between high-temper-
ature stars and low-temperature nebulae.
The latter behave like automatic Maxwell
demons, because molecules that escape
from nebulae eventually are captured by
stars and contribute energy to them as
they fall in, thus helping to maintain the
high temperatures of the stars. To ex-
plain why stars like the Sun do not seem
to be gaining mass by this process,
Arrhenius postulated in addition that
they eject molecules by radiation pres-
sure.

In his paper on the “Arrhenius demon,”
Poincare showed that a more careful
analysis of the physical effects involved in
Arrhenius’s scheme leads to the opposite
conclusion: the Second Law cannot be
violated in this way. But he left open the
possibility that some other mechanism
could be found to accomplish the same
purpose.

Origin of the solar system

By this time (1911), Poincare had
turned his attention from ends to begin-
nings. His book on cosmogonical hy-
potheses is generally regarded as a classic
by workers in this field; it contains the
first serious attempt (aside from that of
Edouard Roche) to give a comprehensive
analysis of the properties of models based
on Laplace’s nebular hypothesis. As a
review of theories of the origin of the solar
system it is well worth reading even today,
but somewhat unsatisfactory because it
ignores some of the most important the-
ories proposed at the beginning of the
20th century, in particular the tidal-pla-
netesimal hypothesis of the American
cosmogonists T. C. Chamberlin and F. R.
Moulton, published in 1905. Poincare
does not take seriously the major objec-
tions to the nebular hypothesis, and pays
little attention to the binary-collision or
tidal-disruption theories that were pop-
ular at the time he wrote. (Lest the
reader think this is a Whiggish criticism
of Poincare, I should remark that the bi-
nary theory was rejected around 1935, and
recent theories again postulate a primeval
nebula.)

If a homogeneous nebula contracts and
spins off rings that condense into planets,

the result should be a central body that
rotates much more rapidly than does our
Sun at present. In other words, if angular
momentum is conserved in the process, it
is difficult to understand how the major
planets rather than the Sun came to have
most of the angular momentum of the
system. That difficulty had been men-
tioned by Jacques Babinet in 1861 and by
Maurice Fouche in 1884, but they con-
sidered it an argument for assuming that
the nebula was initially highly condensed
toward the center rather than as a decisive
objection to the nebular hypothesis itself.
Poincare seems to have adopted their
conclusions without realizing that the
condensed-nebula model was vulnerable
to other serious objections. He does not
even mention the 1900 papers of Cham-
berlin and Moulton, which persuaded
most astronomers to abandon the nebular
hypothesis, or their alternative theory,
proposed in 1905, which was favorably
received by many American and British
astronomers before 1911. (The Cham-
berlin-Moulton theory postulated a close

encounter of the Sun with another star,
drawing material out of the Sun by tidal
forces; the material first solidified to small
particles, which then formed planets by
accretion.18)

Poincare suggested that a homogeneous
nebula, rather than forming a planetary
system by Laplace’s process, would evolve
through the pear-shaped figures he had
investigated in 1885, and then split into
a double-star system as proposed by T. J.
J. See and G. H. Darwin.19 A similar
process might also be responsible for the
birth of the Moon from the Earth. While
he was aware of Lyapunov’s proof of the
instability of the pear-shaped figures, he
did not realize that this proof made them
irrelevant to astronomical evolution.

Ironically one of Poincare’s results on
the stability of a fluid ring, which he in-
terpreted as proof that such a ring could
be formed in the fashion suggested by
Laplace, was used to reach exactly the
opposite conclusion by James Jeans.19
(Jeans favored a tidal theory similar to
that of Chamberlin and Moulton.) I

Henri Poincare

Jules Henri Poincare (1854-1912) came
from a prosperous middle-class family in
Nancy. His cousin Raymond Poincare was
several times prime minister of France and
its President during World War I. Though
sometimes regarded as the world’s greatest
mathematician during his own lifetime, Henri
was not a child prodigy and always had dif-
ficulty with arithmetic. He took a degree in
mining engineering but soon established
himself as a mathematics professor in Paris,
where he remained from 1881 until his death.
His eyesight was bad and his handwriting
terrible; he didn’t bother to revise or polish
his hastily written lecture notes before pub-
lishing them; yet Poincare was one of the
most successful scientists of all time in
communicating his ideas to the public.
(Four paperbacks of his essays were avail-
able until recently from Dover.)

Poincare’s pathbreaking researches in
complex-variable theory, differential equa-
tions and combinatorial topology earned him
an undisputed and continuing high reputation
in pure mathematics. The value of his
contributions to modern physics is less
certain; recognizing the crisis that threatened
to undermine nearly every previously-ac-
cepted law of nature at the turn of the cen-
tury, Poincare was reluctant to propose
radical solutions, and preferred to modify the
existing theories, which he sometimes re-
garded as no more than conventions. When
he reported Wilhelm Rontgen's work on x
rays to the Paris Academy of Science, he
offered speculations that now seem pedes-
trian but apparently inspired Henri Becquerel
to begin the research that led him to discover
radioactivity. When he undertook an elab-
orate development of H. A. Lorentz’s theory
of electrons, he derived much of the math-
ematical structure of relativity theory but
retained the ether hypothesis, relinquishing
to Albert Einstein the glory of discovering the

physical significance of the relativity prin-
ciple. Poincare’s masterpiece on celestial
mechanics was not translated into English
until 1967, when the needs of the space
program made it a valuable reference work
for NASA.

For students of the psychology of science,
Poincare's most memorable publication is
the chapter on "Mathematical Discovery" in
Science and Method. Recalling his own
research on what he called "Fuchsian
functions” in honor of the German mathe-
matician Lazarus Fuchs, he described three
episodes of intensive effort leading to an
impasse, followed by a period when his
conscious mind was occupied by non-
mathematical thoughts. In each case an
important new idea suddenly came to him
with great clarity and certainty, obviously the
result of an unconscious process in which
many possible combinations have been tried,
and a single fruitful one had emerged as a
candidate for detailed calculation and veri-
fication. The process of unconscious ma-
nipulation and selection, he argued, could not
be purely mechanical but must depend on a
"special aesthetic sensibility” that recog-
nizes the most beautiful or harmonious
mathematical entity from among billions of
possible alternatives.

In contrast to his cousin who pursued a
vindictive policy against Germany after World
War I, Henri Poincare demonstrated a special
appreciation for the works of German
mathematicians. When Felix Klein pointed
out that he had considered Poincare’s ”Fu-
chsian functions" though Fuchs himself had
not, Poincare graciously gave the name
"Kleinian” to the next class of functions
which he discovered. Thus Fuchsian func-
tions are those not studied by Fuchs while
Kleinian functions are those not studied by
Klein; the properties or both were in fact
determined primarily by Poincare.

BEFORE OUR TIMES

49

suppose the moral of this example, and of
Poincare’s excursions into cosmic evolu-
tion in general, is that sound mathemat-
ical work can indeed have an impact on
science, but not necessarily in the way
anticipated by the mathematician him-
self.

In summary, I think Poincare’s view of
cosmic evolution was characteristic of the
late 19th century: processes in the
physical world are gradual and irrevers-
ible; discontinuous changes obviously
occur, but only when really necessary and
then not in a catastrophic manner. The
results of mathematical calculation could
be interpreted to support such a view, but
could not provide a proof strong enough
to withstand the onslaught of the revolu-
tionary events and theories of the 20th
century. As I have suggested elsewhere,20
the year 1905 was the turning point in
several areas of science, heralding radical
changes. To a lesser extent one may
claim that Poincare’s concept of cosmic
evolution was undermined by develop-
ments in that year: Lyapunov’s proof of
the instability of pear-shaped figures,
Einstein’s theory of Brownian movement,
and the Chamberlin-Moulton theory of
the origin of the solar system. What
these three have in common is the idea of
catastrophe or random collision, admin-
istering a shock treatment to the 19th-
century idea of a stable, slowly evolving
universe. The mathematician who wants
to be a naturalist must now assimilate a
new set of physical concepts; the need for
mathematical expertise is greater now
than ever before.

This paper is based on research supported by
the History and Philosophy of Science Pro-
gram of the National Science Foundation. I
am indebted to Arthur I. Miller for suggestions
on an earlier draft, to John Blackmore for
sending me copies of the Poincare-Darwin
correspondence, and to William K. Rose for
information on current research in astro-
physics.

References

1. The basic source for Poincare’s technical
articles is Oeuvres de Henri Poincare,
Gauthier-Villars, Paris (1951-1956); see
also Figures d'Equilibre d’une Masse
Fluide, Naud, Paris (1902), and Leqons sur
les Hypotheses Cosmogoniques, second
edition, Hermann, Paris (1913).

2. T. B. Jones. The Figure of the Earth, Co-
ronado Press, Lawrence, Kansas (1967); H.
Brown, Science and the Human Comedy,
University of Toronto Press, Toronto
(1976), chapter 8; I. Todhunter, A History
of the Mathematical Theories of Attrac-
tion and the Figure of the Earth, from the
Time of Newton to that of Laplace, re-
print of the 1873 edition, Dover Publica-
tions, New York (1962).

3. W. Thomson, P. G. Tait, Treatise on
Natural Philosophy, Clarendon Press,
Oxford (1867); second edition, Cambridge
University Press, Cambridge (1879-1883).
J. Levy, “Poincare et le Mecanique Ce-
leste,” lecture at The Hague, 1954, pub-
lished in Oeuvres de Henri Poincare, Vol.
11, pages 225-232.

4. G. H. Darwin, Mon. Not. Roy. Astr. Soc. 60,
406 (1900), page 411.

5. G. H. Darwin, Phil. Trans. Roy. Soc. Lon-
don 170, 447 (1879), pages 535-536.

6. S. Chandrasekhar, Ellipsoidal Figures of
Equilibrium, Yale University Press, New
Haven (1969), page 12; see also R. A. Lyt-
tleton, The Stability of Rotating Liquid
Masses, Cambridge University Press
(1953).

7. Chandrasekhar, ref. 6, page 1 1.

8. J. P. Ostriker, in Stellar Rotation, A.
Slettebak, ed., Gordon & Breach, New
York (1970), page 147, and in Theoretical
Principles in Astrophysics and Relativity,
N. R. Lebovitz et al., eds, University of
Chicago Press, Chicago (1978), page 59; N.
R. Lebovitz, Astrophys. J. 175, 171 (1972);
R. C. Fleck, Jr, Astrophys. J. 225, 198
(1978).

9. See R. Numbers, Creation by Natural
Law: Laplace’s Nebular Hypothesis in
American Thought, University of Wash-
ington Press, Seattle (1977).

10. J. D. Burchfield, Lord Kelvin and the Age
of the Earth, Science History Pubs., New
York (1975). S. G. Brush, The Tempera-
ture of History, Franklin, New York
(1978), Chapter III; The Kind of Motion
We Call Heat, North-Holland Pub. Co.,
Amsterdam (1976), Chapter 14. L. Bad-
ash, Proc. Amer. Philos. Soc. 112, 157
(1968).

11. For the relation of the recurrence theorem
to Nietzsche’s “eternal return” and other
aspects of 19th-century culture, see Brush,
The Temperature of History, Chapter
V.

12. H. Poincare, Rev. Metaphys. Mor. 1, 534
(1893); quotation from the translation in
S. G. Brush, Kinetic Theory, Vol. 2, Per-
gamon Press, New York (1966), page
205.

13. Brush, ref. 12, page 206.

14. For translations of the Zermelo and
Boltzmann papers see Brush, Kinetic
Theory, Volume 2.

15. Oeuvres de Henri Poincare, Vol. 8, page
538: translation in Nature, 58, 183 (1898).
|The printed text says, twice, entropy al-
ways decreases ]. The long quotations in
the text are from Nature, 58, 184-185
(1898).

16. H. Poincare, Congress of Arts and Science,
Universal Exposition, St. Louis, Vol. I,
Houghton, Mifflin & Co., Boston (1905),
pages 604-622, quotation from page 610.
Reprinted in The Monist, 15, 1 (1905).

17. See Brush, The Kind of Motion We Call
Heat, pages 669-700.

18. For further details on this theory and its
history see S. G. Brush, J. Hist. Astron. 9,
1, 77 (1978).

19. H. Poincare, Leqons sur les Hypotheses
Cosmogoniques, pages 22-23; J. H. Jeans,
Problems of Cosmogony and Stellar Dy-
namics, Cambridge University Press,
London (1919), pages 147-153; see also G.
P. Kuiper, J. Roy. Astron. Soc. Canada 50,
105 (1956).

20. S. G. Brush, in Rutherford and Physics at

the Turn of the Century (M. Bunge, W. R.
Shea, eds.), Science History Pubs., New
York (1979), page 140. □

See also S. G. Brush, “From Bump to Clump: Theories of the Origin of
the Solar System 1900-1960, ” in P. A. Hanle and V. D. Chamberlain,
eds.. Space Science Comes of Age (Washington, 1981) pp. 78-100 ;
Brush, “Nickel for Your Thoughts: Urey and the Origin of the Moon,
Science 217 (1982), pp. 891-898; Brush, Statistical Physics and the
Atomic Theory of Matter from Boyle and Newton to Landau and On-
sager (Princeton, 1983), Ch. II.

50

HISTORY OF PHYSICS

Steps toward the
Hertzsprung-Russell Diagram

In the late nineteenth century, astronomers seeking to classify
stars by their spectra using then-current concepts of stellar evolution
found a temperature-luminosity plot that revolutionized the subject.

David H. DeVorkin

PHYSICS TODAY / MARCH 1978

Every student of stellar astronomy en-
counters the fundamental relationship
expressed by the Hertzsprung-Russell
Diagram. One cannot effectively discuss
stars — how they are born, live and die,
how they are distributed in space and how
our Sun fits amongst them — without
using this relationship as a fundamental
tool of communication.

The Diagram, now almost seventy years
old, is today seen in many forms. Basi-
cally it is a plot of stellar energy output
against stellar surface temperature (see
figure 1). The majority of stars plotted
occupy a well-defined diagonal band, with
a secondary grouping along the top. The
observation, first made unambiguously by
Ejnar Hertzsprung in 1905 and then by
Henry Norris Russell in 1910, was that
fainter stars are, on the average, redder
than bright ones — except for those
prominent stars grouped at the top of the
diagram. Astronomers were on the verge
of discovering this relationship for quite
some time, effectively from the early
1890’s. What kept this discovery from
being realized and exploited earlier? We
will see that the observations necessary to
identify stars of similar spectral type, but
of vastly differing luminosities — today
identified as “giants” and “dwarfs” — were
not available until after the turn of the
century. As I shall show, 19th-century
astronomers were unable to detect the
existence of giants and dwarfs among
stars of the same spectral type, which led
them seriously astray.

But to say that astronomers needed
only to produce adequate data before the
diagram was possible is an oversimplifi-
cation. In fact neither Hertzsprung nor

David DeVorkin is presently on leave from
Central Connecticut State College as consultant
to the Center for History of Physics, American
Institute of Physics.

Russell looked directly for the relation-
ship. Each came to it from independent
directions, and with different interests.
But both required very much the same
data base — the brightnesses and spectra
of stars — and so both had to turn to a
single critically important source: Har-
vard College Observatory and E.C. Pick-
ering.1

The meaning of stellar spectra

The origins of the Hertzsprung-Russell
Diagram have one common theme: the
understanding of the meaning of the dif-
ferent spectra seen amongst the stars.
Since the 1860’s and the time of Gustav
Kirchhoff, astronomers engaged in spec-
tral classification, including Angelo Sec-
chi, Hermann Carl Vogel, J. Norman
Lockyer and William Huggins, all held to
the same basic observation that of all the
stars examined (which by the 1880’s had
amounted to several thousands) only a
few basic types were to be found, though
variants existed. Astronomers then as
now were fascinated by the variants —
stars that had variable spectra or stars
with bright-line spectra. But on the
whole, the meaning of the variation of
spectra among the few normal groups was
the primary question. Throughout the
late 19th century the possibility that
composition differences were the cause
was a persistent theme but the pervading
uniformitarian philosophy of Nature, and
the fact that the stars did arrange them-
selves into so few fundamentally different
groups, were strong arguments for some
other explanation. Secchi in the 1860’s
and 70’s, and Lockyer after him, worked
hard to establish temperature as the pri-
mary variable causing changes in spectral
type. To most, however, the simple cor-
relation of spectrum with stellar color was
somehow at the base of the differences
seen in spectra.

But there was a problem with this ap-
parently simple picture. The trouble was
that at the time, in what was a highly
empirical subject, this problem was itself
far from being empirical. Very few as-
tronomers of the late 19th century could
approach the question of the meaning of
stellar spectra without being influenced
by the idea that stars were mechanisms
that radiated energy from a finite store
and hence experienced a continual pro-
cess of aging. This process became
known as the “evolution” of a star, ter-
minology inspired by the Darwinian rev-
olution but in its usage somewhat mis-
leading. And since astronomers had
concluded that all sources of energy —
chemical, electrical or meteoritic — were
inadequate or impossible, only the process
of the cooling of an incandescent sphere
undergoing continual gravitational con-
traction, thereby converting mechanical
energy into heat, was thought possible.

The cooling process was thought to be
directly visible through the spectral dif-
ferences seen among stars. Thus when
astronomers set about examining stars for
their spectra, and began looking for an
appropriate system for their classification,
just about all the systems devised began
with blue stars. Blue stars were appar-
ently the hottest, and had the simplest
spectra. These stars were also most
closely associated with gaseous nebulae in
space, and had spectra quite similar to
nebulae (exhibiting dark-line spectra with
the same groupings and sequences found
in parts of the bright-line nebular spec-
trum). The process of contraction of blue
stars from nebulae was supposed to con-
tinue to the yellow stars (solar type), and
finally, in the general cooling process, to
the red stars and then to extinction. This
order from blue to red was followed by all
the major and popular classifications,
with but a few exceptions, which we shall

BEFORE OUR TIMES

51

The Hertzsprung-Russell Diagram with the
observed stellar spectral classes on the
Harvard System plotted against stellar
luminosity, or total energy output (Sun = 1).

There is a well-defined relationship between a
star's surface temperature and its energy
output. But, as can be seen from the
diagram, each of the redder stars may have
one of at least two possible luminosities for
its spectral class. The failure to recognize
this feature led 19th-century astronomers
astray in their attempts to search out
empirical relationships among the various
parameters that describe the physical
characteristics of stars. Figure 1

identify later in the course of this article.

As spectra became better identified,
and especially when larger telescopic ap-
ertures allowed for an increase in the
dispersive powers of the attached spec-
troscopes, many peculiarities in individual
spectra became apparent. One of the
most important of these was the early
recognition by Secchi of two distinct types
of spectra among red stars. In these two
red classes, banded structure that ap-
peared in the same positions exhibited
different structure. Secchi thought that
the differences were enough to warrant a
separate class, which he tacked on to his
system as a fourth class. Thus his first
class were the blue stars, his second were
the solar type yellows, and his third and
fourth were the reds. Vogel, however,
believed that this separation was too
great. In his system of classification,
which he developed from 1874 through
1895, he retained only the three major
classes, very much as defined by Secchi,
but used subdivisions for what he con-
sidered to be secondary spectral distinc-
tions. Vogel based his classification
system directly on stellar evolution, and
felt that the two classes of red stars were
explained by minor variations in compo-
sition. Lockyer, however, advocated
Secchi’s original separation. He believed
that Secchi’s first red class, class III, ex-
hibited bright lines and hence made them
closer in evolutionary stage to nebulae
than were the blue stars. Secchi’s class
IV stars, in Lockyer’s minority view, were
furthest removed from nebulae, and
hence occupied the classic evolutionary
place of red stars.

Lockyer favored Secchi’s system be-
cause he was one of the very few who did
not follow the popular concept of evolu-
tion. In Lockyer’s view stars passed
through the temperature sequence twice,
ascending in temperature from a cold

ID*

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• •

10!

10

10

Giants and supergiants

,.v,«44*w’

Main sequence (dwarfs)

F G

SPECTRAL TYPE

nebular state and then, after attaining a
maximum temperature as a blue star,
cooling to extinction through the normal
color and spectral progression. Even
though there was much in Lockyer’s
scheme that can be seen at subtler levels
in the evolutionary schemes of the ma-
jority of astronomers of the time — those
represented best by Vogel and
Huggins — Lockyer’s zeal in connecting
his temperature arch (see figure 2) with

his belief that nebulae were swarms of
meteors in collision, and that all stars on
his ascending branch were condensing
meteoric swarms, kept his views quite
unpopular throughout the latter half of
the 19th century.-

From the theoretical side, Lockyer’s
model for stellar evolution was antici-
pated by the studies of J. Homer Lane of
Washington, D.C. and of August Ritter of
Potsdam who, between 1870 and 1883,

Norman Lockyer’s “Temperature Arch,” which first appeared in the late 1880’s. Lockyer’s
elaborate classification system is represented by generic archetypes. Within the arch we have
bracketed the region where a significant number of stars examined for parallax (and hence for lu-
minosity) by Russell and Hinks were also included on Lockyer’s later lists. Clearly these stars,
while exhibiting similar temperatures, must differ greatly in other characteristics. Figure 2

52

HISTORY OF PHYSICS

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Part of a letter from Hertzsprung to Pickering dated 15 March 1906.
Here Hertzsprung shows that in the redder classes, the two sequences
of stars (Antonia Maury's spectral classifications "c” and “non-c,''
proposed in 1897) differed by greater amounts in absolute magnitude.

1

The listing reads left to right in columns. Reproduction from the E. C.
Pickering Collection, Harvard University Archives. The photograph of
Hertzsprung on the right is reproduced by courtesy of Dorrit Hoffleit, Yale
University Observatory. Figure 3

discussed the behavior of contracting gas
spheres in convective equilibrium. Their
independent findings showed that such
bodies, beginning their lives as perfect
gases, first heated upon contraction and
began a cooling process only when densi-
ties within their interiors reached levels
that caused them to deviate from the
perfect-gas laws.3 These works began to
be noticed generally by astronomers in the
1890’s and caused considerable conster-
nation in those, especially Huggins, who
wished to reconcile them with the ob-
served sequence of spectra.

Aside from difficulties reconciling
theoretical arguments with observation,
the observations themselves left much to
be desired. Lockyer’s belief in the pres-
ence of bright lines in some red stars was
symptomatic of the great difficulty of in-
terpreting visual stellar spectra. In the
1880’s photography began to rectify the
situation, but even then, astronomers
found that the highly limited sensitivity
and poor reproducibility of photographic
emulsions kept the new technique from
causing an overnight sensation. It was
also painfully evident that most of the
prevalent classification schemes could
well be fortuitous, and fraught with se-
lection effects. The persistence of these
crucial limitations in technique and
completeness was in keeping with the
status of the rest of the astronomical data
base. Systems for determining the
brightness of stars were far from
standardized, and very few stars had re-
liable trigonometric parallaxes to deter-
mine their distances.

Such was the situation in stellar as-
tronomy when Pickering, then a young
physicist at MIT, accepted a post as the
new director of Harvard College Obser-
vatory in 1877. In the 1880’s Pickering
began to organize two large projects with
generous support from the family of
Henry Draper and others, to improve the

situation. He established an objective-
prism survey of the spectra of stars visible
from Cambridge and Arequipa, Peru, and
developed an accurate and consistent
scheme for the determination of the ap-
parent brightnesses of stars.

The use of objective prisms, thin prisms
placed in front of the objective lenses of
telescopes, was not new to Pickering.
Both Joseph Fraunhofer and Secchi had
used this efficient means of securing
spectra. But Pickering attached these
prisms to wide-field photographic astro-
graphs, and thereby was able to secure
spectra of hundreds of stars in one expo-
sure. These exposed plates yielded the
spectral classes of thousands of stars
through direct eye examination in the
rooms of the Harvard College Observa-
tory, a comparatively mild environment
compared with the cramped and often
frigid confines of the telescope dome.

Pickering’s projects were made possible
by the enthusiastic and untiring assis-
tance of a corps of women, headed by
Wilhaminia P. Fleming. By 1890, he and
Mrs Fleming brought out the first Henry
Draper Catalogue of Stellar Spectra
containing some 10 000 stars.

Pickering devised a simple alphabetic
scheme of classification based upon the
visibility of the hydrogen lines. Class A
showed hydrogen lines strongest, and the
series ranged on to 0, P and Q. Refine-
ments followed with more and better
spectra. By 1898 he and a new assistant,
Annie J. Cannon, who worked with
Fleming, decided that the order must be
reversed to 0,B,A,F,G,K,M, primarily
because O and B stars had similar helium
spectra and both were closely associated
in space with nebulae. This was a most
important reversal in the classification
system (which appeared in 1901) for it
demonstrates the influence of evolution
upon the Harvard classifiers. The fact
that the Harvard classification has since

turned out to be a highly accurate tem-
perature classification appears therefore
to be fortuitous. It has, however, re-
mained standard to this day.

But Pickering had long realized that
the average quality of each of the tens of
thousands of stars his team had been
classifying was at best rough. Stellar
spectra were far more complicated than
the single objective prism could reveal,
and therefore warranted closer attention
along the lines advocated by the pioneers
Huggins and Vogel. Pickering therefore
designed, as a corollary project, an ex-
amination of a few bright stars under
higher dispersion. Antonia Maury,
Henry Draper’s niece and one of the few
women at that time actually trained in
astronomy and physics, was delegated the
task, and through the 1890’s from a small
but high quality sample of stellar spectra
she devised an extremely sophisticated
system of classification.

In 1897 Maury proposed her new sys-
tem of classification. It had 22 numerical
groups and identified differences within
many of these groups in terms of relative
line strengths and line widths. In brief,
she detected two primary subdivisions:
stars with normal spectra (hydrogen lines
broad) designated a and b; and stars with
especially sharp hydrogen lines and with
metallic lines somewhat enhanced, des-
ignated c and ac. She later identified
these two subdivisions as “c” and “non-c”
in character. Maury noted that the ex-
istence of the subdivisions within several
of her numerical groups suggested the
existence of “parallel courses of develop-
ment.” Her provocative words were not
heeded at the time. Indeed, her work
remained unnoticed until Hertzsprung
decided to find out if the two subdivisions
she had detected represented anything
uniquely interesting in the physical
properties of the stars themselves.

But Hertzsprung’s work can only be

BEFORE OUR TIMES

53

In Russell's lecture notes dated 14 March 1907 the upper curve represents Lockyer’s view, where
Type I are blue stars, Type II, yellow, and Type III. the red stars. Russell’s second curve represents
the classical cooling line, and is strikingly similar to what one would expect from a main sequence.
Russell commented on these two curves noting ... we cannot be sure at present though some
things look as it the first hypothesis is correct ..." Reproduction from the Henry Norris Russell
Papers, Princeton University Library. Figure 4

appreciated within its context, the sta-
tistical examination of the spatial distri-
bution of spectra, which was a growing
interest in astronomy since 1890.

Spatial distribution of spectra

Secchi and a few others had long real
ized that stars of his first class (blue stars)
tended to be concentrated more towards
the Milky Way plane than were stars of
other classes. By 1890, this concentration
had been noticed also for bright -line stars,
but significant statistical studies began to
appear only with the availability of the
Henry Draper ( 'atulogue. These studies
had two major themes: 'The analysis of
the structure of the sidereal system, and
the nature of the stars themselves.
Which were the most luminous stars, and
which were the least? Which were the
largest in radius and which were the
smallest? Clearly, an analysis of the
mean distances of the different spectral
classes, when compared to their mean
relative apparent brightnesses, would
yield statistical information about their
relative actual brightnesses and sizes
(neglecting by necessity any differences
due to relative emittance as a function of
color or spectral class). It must be re-
membered that relative size implied rel-
ative age, because the only conceivable
direction of evolution, on whatever
scheme, was contraction. To astrono-
mers of the turn of the century therefore,
such studies could yield information
about the evolutionary status of the dif-
ferent spectral classes.

'The first distribution studies were also
the simplest, correlating spectral type
with position on the celestial sphere. But
later studies correlated apparent motions
too, and when examined statistically,
these yielded mean distances.

W.H.S. Monck, an Irishman about
whom little is known, was one of the first,
along with the legendary -l.C. Kapteyn, to
examine stars in this manner, correlating
proper motions with spectra to determine
mean distances and hence mean intrinsic
brightnesses. When Monck sat down to
the task of comparing the data at hand he
found, in 1892, that proper motions in-
creased with advancing (blue to red)
spectral type, except that the reddest
stars did not, as a group, have the largest
motions; the yellow stars did. Monck
concluded that the yellow stars must, as
a class, be the closest to the Sun. He went
so far to suggest that the Sun might be in
a small cloud of solar-type yellow stars.
But the fait remained that when he
compared their distances and mean ap-
parent brightnesses to the corresponding
quantities for the other spectral classes,
the solar-type stars came out the least
luminous intrinsically. 'This meant that
there were red stars brighter, and possibly
larger, than the Sun. By 1898, not only
Monck hut also Kapteyn had come to this
conclusion. Monck thus altered the
“normal" course of evolution by placing

the red stars of classes K and M before the
solar-type (1 stars. In this he clearly was
following the dictum of contraction, in
spite ot the tact that it played havoc with
the accepted temperature history of
stars.

In the next year, J.K. (lore, a friend of
Monck's, showed in a popular text titled
The Worlds of Space that there were red
stars of great dimension. Using proper
motions and brightness and neglecting
colors, (lore found that these “giant stars”
as he called them (borrowing terminology
initiated by R.A. Proctor) were, as in the
case ot Arcturus, some 80 times the Sun’s
diameter or about the size of Venus's
orbit. Thus, if (lore’s calculations were
anywhere near correct, how could solar
stars cool and contract into red stars when
there were red stars far larger than the
Sun? These bright red stars at least
could not have succeeded the yellow or
blue stars, and must necessarily be quite
young in their life histories, (lore did not
mention the theories of Loekver or Lane
and Ritter, which would have supported
his findings, but Monck did consider
briefly the possibility of giant stars in his
later work. He could not press the ques
tion, for he considered his data base too
weak. Though spectra had become
plentiful enough by that time, consistent
measures of distance (and hence lumi
nosity) from proper motions were still
lacking, and tar too few direct trigono-
metric parallaxes were available for any
proper statistical analysis.

Monck therefore was not able to Lake
the step taken by Hertzsprung just a few

years later, when for the first time it was
found that the reason red stars had
greater mean brightnesses was the inclu-
sion among them of giant stars. It is quite
clear today that Monck’s and Kapteyn 's
samples were affected by the great visi-
bility of red giant stars. Though they are
quite rare in space, they were the only red
stars bright enough to be easily photo-
graphed for spectra.

In 1900 the problems just discussed in
statistical astronomy were very much
open. The proliferation of spectral clas-
sification schemes, and their interpreta-
tion, frustrated many. Further confusion
came from a general lack of consensus
over the physical meaning of spectra. It
had long been believed that the normal
spectral sequence revealed the tempera-
ture history of stars, with slight variations
due to composition. But by the late
189()’s. other physical variables such as
density and atmospheric pressure de-
manded serious consideration as the pri-
mary causes. There were those, including
the illustrious William Huggins, who felt
that extensive masking by the stellar at-
mosphere, dependent upon atmospheric
density, was the primary factor. In 1900
he suggested that selective absorption by
an extensive stellar atmosphere might be
great enough to cause a blue star to ap-
pear red. He saw the red stars as the
most advanced in life, and therefore the
densest. By Lane’s law, they should also
be the hottest, thought Huggins, who for
some reason seemed to think that the
stars remained perfectly gaseous
throughout their lives. Thus, he intro-

54

HISTORY OF PHYSICS

VISUAL MAGNITUDE

One of the first diagrams published by Hertzsprung for the Hyades star cluster, adapted from
Potsdam Publications 22 (191 1), page 29. The horizontal coordinate represented apparent mag-
nitude, the vertical one Hertzsprung’s ''color-equivalent,” a measure of stellar color. Figure 5

duced masking to argue that the red stars
were, in fact, the hottest, but appeared the
coolest due to their selectively absorbing
atmospheres. Huggins’s ideas helped to
confuse the interpretation of spectra, and
hence it remained quite difficult to apply
the radiation laws of Josef Stefan, Wil-
helm Wien and Max Planck to the
stars.

Ejnar Hertzsprung

Happily this situation did not stop the
young Danish photochemist Ejnar
Hertzsprung. As one of his earliest in-
terests in astronomy, Hertzsprung ap-
plied the laws of radiation to find, in 1906,
that Arcturus (the same star singled out
by Gore) was the size of Mars’s orbit. At
the same time he also revived the statis-
tical studies of Monck and Kapteyn, and
entered directly upon the work that led
him to construct the first “Hertzsprung-
Russell” Diagram.

But what was it that allowed
Hertzsprung to rediscover what Monck
and Kapteyn had found but could not
exploit? Hertzsprung stated at the out-
set of his first statistical study in 1905 that
it was Maury’s classification system that
stimulated his interest in searching for
what determines the differences in spec-
tra among the stars. In particular he
wanted to know why there were subdivi-
sions among her spectra (a,b; c and ac).
Hertzsprung began, as had Monck and
Kapteyn, using proper motions statisti-
cally to derive relative distances and rel-
ative brightnesses for the different spec-
tral classes. But, unlike the others, he
had Maury’s classification as a guide.

In his first analysis he found, as did the
others, that the major spectral classes
exhibiting greatest proper motion were
the solar classes and not the red classes.
But after a detailed analysis of the various

groups defined on Maury’s system he
found that for all stars brighter than
magnitude +5 the red ones had van-
ishingly small proper motions, and only a
very few had parallaxes. But among stars
of large proper motion or parallax he
found mostly faint red and yellow stars.
Hertzsprung was particularly intrigued
that the former group contained c stars,
and the latter, non-c stars. What made
Hertzsprung’s analysis extremely difficult
was that, for the redder classes, the sub-
divisions were not distinct at all; so he had
to construct an elaborate indirect process
of analysis that allowed him to come to
this conclusion.

Nevertheless, triggered by Maury’s
classification, Hertzsprung had found a
filter by which he could distinguish in-
trinsically bright and faint red stars, de-
pending upon which proper motion and
brightness group they fell into. After he
established the technique, he concluded
that the total sample of yellow stars ap-
peared fainter because there was a greater
proportion of dwarf yellows relative to
giant yellows in it. This was due to the
fact that the dwarf yellows were just a bit
brighter than the dwarf reds, and there-
fore appeared more frequently in general
surveys.

After the publication of his first paper
on the subject, in an obscure German
photographic journal, Hertzsprung wrote
to Pickering in March 1906 discussing his
work and the resulting significance of the
Maury system of subdivisions, which
could now be used to detect luminosity
differences wherever the subdivisions
were distinct. Within this letter was a
descriptive table outlining how he felt the
c and non-c spectra should be examined
so as to illustrate the great luminosity
differences between them (see figure 3).

During 1906 Hertzsprung continued his

work, and in 1907 he published a second
paper with a slightly different selection of
stars. Here he was concerned with re-
fining the magnitude differences between
the c and non-c stars by incorporating
reliable parallax data, where available.
He also discussed the space densities of
stars in each class, finding correctly that
giants of all classes were rare. With this
second paper, Hertzsprung’s local repu-
tation grew. He had become a close
friend of Karl Schwarzschild4 and as a
result followed Schwarzschild from Got-
tingen to Potsdam as a staff astronomer
when the latter became the director there.
But Hertzsprung’s international reputa-
tion had not yet been made, even though
his papers and letters were in Pickering’s
hands.

In 1908 when Hertzsprung received a
copy of the latest Harvard Annals he re-
alized with some surprise that Pickering
had not taken his 1906 letter and 1905
paper seriously, for Maury’s spectroscopic
notation and subdivisions had not been
reinstated in the publication (they were
dropped in the 1901 Harvard Annals in
Cannon’s extension of the original al-
phabetic system). Hertzsprung wrote5 to
Pickering in July 1908 to voice his concern
over the apparent neglect of so important
a discovery:

It is hardly exaggerated to say that
the spectral classification now adopt-
ed is of similar value as a botany,
which divide the flowers according to
their size and color. To neglect the
c-properties in classifying stellar spec-
tra I think, is nearly the same thing as
if the zoologist, who has detected the
deciding differences between a whale
and a fish, would continue in classi-
fying them together.

Hertzsprung wished that Maury’s classi-
fication system would be reinstated so
that stars of great luminosity could be
identified. In early August Pickering
responded cordially but skeptically, not-
ing that he did not have enough faith in
his own spectra to believe in Maury’s
subdivisions. He felt that the objective
prism spectra she had used did not have
the resolution or standardization one
would need to be able to determine real
differences in line structure, since slight
instrumental changes could easily change
the appearance of the lines. Pickering
believed that her line differences could
only be confirmed by the use of high-
quality spectra taken with slit spectro-
graphs— a conclusion he had first voiced
in print in 1901.

It is understandable that Pickering
would be very cautious about using
Maury’s subdivisions. At the time, his
main concern was putting the general
Harvard Spectral Classification system on
a sure footing in the astronomical com-
munity. At the time no system was gen-
erally preferred, and many of Pickering’s
colleagues, for example George Ellery
Hale, continued to use the earlier systems

BEFORE OUR TIMES

55

of Secchi and Vogel. Pickering was all
too aware of the inconsistencies found in
many classification systems that had tried
to say too much in the past, and strove to
keep his own as simple and unambiguous
as possible. Still, after 17 years and tens
of thousands of stars classified, there was
no generally accepted standard.

But this did not comfort Hertzsprung.
He had also noticed that in addition to
line-width variations, line ratios in the two
subdivisions were different. Further, as
he wrote back to Pickering arguing his
point:6

The fact that none of the stars
called c by Antonia Maury has any
certain trace of proper motion is, I
think, sufficient to show that these
stars are physically very different
from those of divisions a and b.

By October 1908 Hertzsprung sent a new
manuscript to Pickering before he sub-
mitted it to the Astronomische Nachri-
chten. In private to Schwarzschild he
had expressed his bitter disappointment
over Pickering’s attitude7 but to Pickering
he maintained a diplomatically firm air,
noting that his paper was intended for
publication with or without Pickering’s
approval. If, however, Pickering wished
to provide commentary, Hertzsprung
would find it most welcome. The Astro-
nomische Nachrichten paper did appear
in 1909, and was a partial restatement and
expansion of Hertzsprung’s earlier work.
These three papers contained tabulated
data sufficient for a Hertzsprung -Russell
Diagram, but no diagrams appeared.
These only came in 1910 and 1911.

To place Pickering’s skepticism into
proper context, we have to provide a fuller
picture of his involvement in the devel-
opment of the diagram, which centered
upon support for the work of Henry
Norris Russell.

Henry Norris Russell

It is not rare in the history of science to
find the most pivotal and crucial discov-
eries and studies made independently by
different people at about the same time.
In many cases the time was right, the need
was apparent, and the discovery was “in
the air." Though there is good evidence
that this is true here, the universal nature
of the diagram allowed for its discovery by
workers interested initially in different
goals.

The influences upon Russell causing
him to come to the diagram, or to the re-
lationship behind it, are quite different
from those upon Hertzsprung. While
Hertzsprung was intrigued by Maury’s
classifications, and attempted to unravel
their meaning hoping for a better under-
standing of the apparently anomolous
statistical behavior of the red stars, Rus-
sell came to the problem primarily from
an interest in evolution stimulated by
Lockyer’s writings.

After a brilliant student career at

Russell’s 1914 diagram. The vertical coordinate
is absolute magnitude derived from his parallax
work. The horizontal coordinate is spectral
class on the Harvard System. The large open
circles along the upper part of the diagram
represent mean absolute brightnesses for bright
stars whose parallaxes were on the order of their
probable errors. All these stars had very small
proper motions, indicating a statistically distant
sample. Adapted from H. N. Russell, "Relations
Between the Spectra and Other Characteristics
of the Stars,” in Popular Astronomy 22 (1914)
page 285, figure 1. Figure 6

Princeton, Russell spent several post-
graduate years (1902-05) studying at
Cambridge University and developing,
with A.R. Hinks, Chief Assistant at the
Cambridge University Observatory, one
of the first photographic parallax pro-
grams ever attempted. Though this was
clearly a pilot program, the 55 stars se-
lected for study included 21 common to a
recently published (1902) list of stellar
spectra by Lockyer. Lockyer had se-
lected only the brightest stars for his
listing, while Hinks and Russell said their
criteria for choosing parallax stars in-
cluded brightness only as a minor con-
sideration. Understandably, they pre-
ferred the more fruitful criteria of large
proper motion and previous parallax
measurement in choices of parallax can-
didates. Thus it is surprising that half
their stars were on Lockyer’s list. Fur-
ther, when one examines the distribution
of stellar types they chose, it is obvious
that the Lockyer stars chosen were just
those that could best test his double-
branched temperature arch (see figure
2).

Russell’s interest in Lockyer’s hy-
pothesis can be seen in lecture notes he
prepared for a course in 1907 at Princeton.
For a lecture in March 1907 on stellar
evolution he first reviewed spectral clas-
sification, then the two possible courses
for evolution, clearly preferring Lockyer’s
(see figure 4). Of great interest, though,

is how he chose to represent the classical
theory due primarily to Vogel. He
showed it as a descending line quite like
what one would expect from a rudimen-
tary representation of the main sequence
in a Hertzsprung-Russell Diagram.
Unfortunately, since Russell did not label
his axes, we cannot say that he knew in
1907 that for main sequence stars,
brightness diminished with increasing
redness. At best, this sketch represents
Russell’s keen intuitive powers.

To exploit his parallax work fully,
Russell needed to reduce his parallaxes to
account for the probable parallactic mo-
tions of the reference stars. For whereas
parallaxes based upon visual meridian
circle measures yielded fundamental po-
sitions and motions relative to the ter-
restrial observer, photographic parallaxes
revealed only motion relative to the se-
lected background reference stars. These
background stars could also have their
own parallactic motions, which would
have to be taken into account before the
actual parallactic motion of the program
star could be determined. To do this
Russell resorted to Kapteyn’s established
technique of statistically derived proper
motions based upon brightness and
spectral class. Thus Russell needed
spectra and magnitudes, best available
from Harvard and Pickering.

It was actually Pickering who ap-
proached Russell, having heard of his
needs.8 This is of interest because, by the
time Russell and Pickering were in con-
tact, Pickering had already received
Hertzsprung’s early paper and arguments
for why the K and M red stars did not, as
a group, have the largest proper motions.
Yet Pickering suggested to Russell in late
April 1908 that Harvard would produce
the spectra of the parallax and reference
stars, and added9: “The material would
perhaps be sufficient to determine which
were the most distant, stars of Class A or
Class K.”

After Russell sent Pickering identifi-
cations for the stars in need of spectra and
magnitude, a long gestation period set in.
By September 1909 Russell had received
most of the data from Pickering and
found at the outset that:

. . .the fainter stars average redder
than the brighter ones. I do not know
of any previous evidence on this ques-
tion ... I would not now risk reversing
the proposition and saying that the
red stars average intrinsically fain-
ter— some of them certainly do; but
Antares and a Orionis are of enor-
mous brightness, and the average may
be pretty high.

These conclusions10 are strikingly close
to Hertzsprung’s and so should have
prompted Pickering to reply with men-
tion of Hertzsprung’s work, if only to state
that Russell had come to the same con-
clusions but from a much more direct and
reliable data base. But Pickering re-
mained silent, quite possibly so skeptical

56

HISTORY OF PHYSICS

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Unpublished Russell diagram clipped to a note from Lockyer to Russell dated June 1913, while
Russell was in London. Russell evidently had this diagram with him when he visited Lockyer.
Russell attempted here to indicate the number of stars found in each magnitude and spectral class
range. The photograph on the left shows Henry Norris Russell as he appeared prior to World War
I. The diagram is reproduced from the Russell Papers, Princeton University Library; the photograph
is in the American Institute of Physics Margaret Russell Edmondson Collection. Figure 7

of Hertzsprung’s use of Maury’s data that
he had decided to keep the matter to
himself for fear of misleading Russell.

The earliest diagrams

It should now be clear that the funda-
mental empirical relationship between
the spectra or colors of stars and their
intrinsic brightnesses was established
independently by Hertzsprung and by
Russell well before it was ever put into the
form of a diagram. Russell had the model
as early as 1907 — if we are allowed to read
between the lines — and could have pro-
duced a diagram easily by 1909. A.V.
Nielsen has shown that Hertzsprung, as
early as 1908, had created a diagram of an
open cluster of stars, but kept it from
publication because of instrumental er-
rors.11

The first diagram to see print was for
the Pleiades cluster, in a paper written in
June 1910 by H. Rosenberg,
Hertzsprung’s assistant at Potsdam.
Hertzsprung’s own diagrams of the
Pleiades and Hyades clusters came soon
after (see figure 5).

Russell first heard of Hertzsprung’s
work from Schwarzschild during a meet-
ing of astronomers at Harvard in August
1910, and in 1911 he wrote to Pickering
suggesting that they might follow up
Hertzsprung’s cluster diagrams with
spectra of the stars he included, instead
of the color-equivalents Hertzsprung was

using. The primary reason for the lapse
of time between 1910 and late 1913 —
when Russell became capable of produc-
ing a diagram and when he actually did
so — was his own concern for the meaning
of the great luminosity difference found
between “giants” and “dwarfs” (termin-
ology he had created while attempting to
describe his findings in correspondence
with Pickering). The differences could be
due to mass or to volume. Russell’s chief
activity in this interval was to establish
that it was a volume difference, from
studies of binary stars he had initiated
and that were carried out by his graduate
student Harlow Shapley. Russell had
earlier developed a method for determin-
ing the densities of eclipsing binaries,
had maintained considerable interest in
stellar densities and binary reductions
all the while, and by 1910 had strong evi-
dence that there were stars of extremely
low density and hence enormous vol-
ume— giant in size but not in mass. While
Shapley continued his own binary star
orbit calculations through 1912, Russell
began to realize that the mass range
among all stars was quite small compared
to variations in other physical character-
istics. Shapley ’s examination of about 90
binary systems helped confirm Russell’s
first results, which then only awaited the
proper opportunity for presentation.
This arose in June 1913, while Russell and
a small band of American astronomers

stopped briefly in London en route to the
summer meetings of the International
Solar Union held in Bonn.

While in London, the Americans were
invited to present results of recent re-
search to the Royal Astronomical Society.
Russell presented his discussion “Rela-
tions Between the Spectra and Other
Characteristics of the Stars” — a title he
had kept prepared for several years. His
paper was brief, due to the usual time
limitations, and did not appear in print
for a few months. Its first appearance
was without the diagrams, though his text
referred to them.

Reactions to Russell's work

Initial reactions to Russell’s work were
positive. Arthur Stanley Eddington
worried a bit at first about Russell’s
thoughts on evolution, which went against
the established grain, but in correspon-
dence he admitted a deep interest and
fascination. Whatever Eddington felt
about Russell’s evolution, which was lit-
erally a revival of Lockyer’s old ideas, he
was sure of the great value of the diagram
(see figure 6) and wanted to publish one
in a book about to see print. While Rus-
sell was in London, he met and discussed
his ideas with Lockyer, who for obvious
reasons was delighted with the turn of
events this American had brought. A
note from Lockyer to Russell (found in
Russell’s papers at Princeton) discussing
this meeting in 1913 was clipped to three
rudimentary Diagrams, and a histogram
picturing the mean apparent brightnesses
of the various spectral classes. I include
one here, for it may be Russell’s earliest
attempt to represent his findings graph-
ically (see figure 7).

In the years following Hertzsprung’s
and Russell’s presentations the Diagram
became better refined. Its primary
function to picture the vast differences
between giants and dwarfs was strongly
supported by the invention and applica-
tion of the technique of spectroscopic
parallaxes, which allowed absolute lumi-
nosities to be determined by a means in-
dependent of trigonometric parallaxes.
In 1920 the angular diameter of a giant
star was measured by A.A. Michelson and
Francis Pease at Mount Wilson and was
found to be very close to predicted
values.

Thus, while the diagram itself remains
as an empirical fact, its interpretation has
changed radically in past years. 1 2 Russell
saw the giant branch and main sequence
as a continuous series of homologously
contracting gas spheres. While they were
giants they behaved as perfect gases and
thus heated upon contraction. But they
turned into relatively incompressible
fluids once on the main sequence — caus-
ing further contraction to result from
cooling only.

The main sequence persisted as an ev-
olutionary track until the mid-1920’s, and
the position of the giants in evolution re-

BEFORE OUR TIMES

57

mained unsolved until the early 1950’s.
Many aspects of theoretical astrophysics
had to develop and mature before our
present interpretation of the
Hertzsprung-Russell Diagram became
possible. In Russell’s time, stars were
purely convective, fully mixed and capa-
ble of contraction only. The many ad-
vances needed to change these 19th-cen-
tury views represent the mainstream of
progress in stellar astronomy over the past
sixty-five years. It is a tribute to Russell’s
memory that he had something to do with
almost all of them.

1 would like to thank the archivists at
Princeton and Harvard Universities, and at
the Lick Observatory Archives, for aiding me
in my research. Material made available by
the AIP Center for History of Physics has
been central to this work. I would particu-
larly like to thank A.J. Meadows of the Uni-
versity of Leicester for his interest and sup-
port for my studies of the history of the
HertzsprungTRussell Diagram.

References

1. See: D.H. DeVorkin, “The Origins of the
Hertzsprung-Russell Diagram” in In
Memory of Henry Norris Russell, A.G.
Davis-Philip, D.H. DeVorkin, eds. (Dudley
Observatory Report No. 13, Proceedings
of IAU Symposium 80, 1977). This book
includes recollections of Russell’s scientific
life by his students, colleagues and histo-
rians. For general background informa-
tion on the topics discussed in this paper
see: B.Z. Jones, L.G. Boyd, The Harvard
College Observatory, Harvard (1971); A.V.
Nielsen, “The History of the HR Diagram”
Centaurus 9 (1963), page 219; D. Her-
mann, “Ejnar Hertzsprung — ‘Zur
Strahlung der Sterne’ ” Ostwalds Klassi-
ker no. 255, Leipzig (1976); O. Struve, V.
Zebergs, Astronomy of the 20th Century,
Macmillan (1962).

2. See: A.J. Meadows, Science and Contro-
versy— A Biography of Sir Norman
Lockyer, MIT (1972).

3. See: S. Chandrasekhar, Stellar Structure,
Dover (1957), pages 176-179.

4. See: Nielsen, ref. 1.

5. Letter, Hertzsprung to Pickering (22 July
1908) Harvard Archives, E.C. Pickering
Collection.

6. Letter, Hertzsprung to Pickering (17 Au-
gust 1908) Harvard.

7. Letter, E. Hertzsprung to K. Schwarzschild
(26 August 1908) Schwarzschild Papers
Microfilm, American Institute of Physics
Niels Bohr Library.

8. See: Jones and Boyd, ref. 1.

9. Letter, E.C. Pickering to H.N. Russell (22
April 1908) Princeton University Library,
Henry Norris Russell Papers.

10. Letter, H.N. Russell to E.C. Pickering (24
September 1909) Harvard.

11. Nielsen, ref. 1, page 241.

12. For an excellent review of the history of the

Hertzsprung-Russell Diagram since its
discovery see: B.W. Sitterly, “Changing
Interpretations of the Hertzsprung-Rus-
sell Diagram, 1910-1940: A Historical
Note,” in Vistas in Astronomy 12, Perga-
mon (1970), page 357. □

59

— Chapter 2

I nstitutions of Physics

Most scientists begin their careers fascinated with pure
scientific knowledge and only gradually come to
understand that discoveries are made by real people. The
history of science likewise had to mature before it could
fully recognize the importance of institutions in the growth
of knowledge. The most important of these institutions, of
course, are the great universities and laboratories, and
they are so important that we can take it for granted that
physicists have at least a rough understanding of how they
came into being and how they function. For other
institutions, understanding is much less widespread.

The organization of the discipline itself often seems like
dull stuff to the average physicist, and usually attracts the
attention of only a few leaders of the field. It is precisely in
attending to such things that they are leaders. The
scientific enterprise would instantly collapse without its
own self-created institutions, which for centuries have
been astonishingly democratic, durable, and unobtrusive.
The articles in this section describing, for example, the
founding of the American Institute of Physics, the

American Association of Physics Teachers, and
institutions in the field of crystallography, should be read
with the thought in mind that without these institutions,
such vital everyday matters as journal publication and
conferences would look quite different and might not even
be possible.

The French entrepreneur of science Jean Perrin
remarked that science may be done with brains, but
"brains, annoyingly enough, are attached to stomachs.”
Feeding those stomachs takes money. The articles in this
section on the Kellogg Radiation Laboratory, on Bell Labs
(a piece which is one of the few detailed case studies ever
written on industrial physics), and on the Office of Naval
Research, show how physics has raised funds for research
by proving its usefulness in medicine, business, and war. In
each case, however, a simple utilitarian appeal was not the
whole story; everyone seems to have recognized that
physics has an appeal and an importance that goes beyond
anything it can immediately deliver.

Contents

61

68

74

78

86

94

The roots of solid-state research at Bell Labs

Some personal experiences in the international coordination of
crystal diffractometry

The founding of the American Institute of Physics

The first fifty years of the AAPT

The giant cancer tube and the Kellogg Radiation Laboratory

The evolution of the Office of Naval Research

. Lillian Hartmann Hoddeson

. P. P. Ewald
. Karl T. Compton
. Melba Phillips
. Charles H. Holbrow
. The Bird Dogs

INSTITUTIONS OF PHYSICS

61

The roots of solid-state
research at Bell Labs

The impact of science on industry — and of industry on science —
is nowhere better illustrated than by the origins of the solid-state group
at Bell Laboratories, which gave the world the transistor.

Lillian Hartmann Hoddeson

PHYSICS TODAY / MARCH 1977

Solid-state physics has experienced a
dramatic growth in the last four decades;
whereas in the 1920’s the term “solid-state
physics” was not yet in use, this is now the
single most populated sub-field of phys-
ics. Much of this growth has taken place
in industry, so that today a small number
of industrial laboratories are producing a
substantial fraction of contributions in
the field.

In this article I explore the roots and
beginnings of basic solid-state research in
one industrial setting, Bell Laboratories,
where crucial advances were made, such
as those leading to modern semiconductor
electronics. By focussing on these de-
velopments we may hope to gain insight
into the mechanisms of the contemporary
impact of basic physics on industry, as
well as into the complementary role that
industrial policies have in turn played in
shaping specific areas of modern re-
search.

The roots of Bell’s solid-state program
developed gradually, in a series of stages
generated by internal technological needs
of the expanding telephone industry.
The stages show a striking reciprocal in-
terplay between science and technology
in the context of corporate expansion.
Let us examine four stages:

1875-1906 A newly invented device es-
tablishes an industry.

1907-24 Technological needs called for
by the growth of the industry lead to in-
house research.

1925-35 Interactions with scientific re-
search outside the Laboratories help focus
some of its basic technical studies on even
more fundamental scientific issues.
1936-45 The intensified focus on scien-
tific underpinnings of technological

Lillian Hartmann Hoddeson is an assistant pro-
fessor of physics at Rutgers University, New
Brunswick, New Jersey.

problems leads to proliferating scientific
and technological developments, among
them the formation of the famous solid-
state group that in 1947 would demon-
strate the first transistor.

Let us recapitulate these stages in more
detail, starting at the tiipe of the inven-
tion of the telephone.

Establishing a telephone industry

In 1876 Alexander Graham Bell re-
ceived a patent for his method of trans-
mitting sounds by electrical undulation,
and in 1877 he patented his “magneto-
telephone,” a device that could actually
transmit speech. The telephone industry
began several months later when the first
telephones were leased to subscribers.

The manufacture, installation and
maintenance of telephones in the growing
business raised new technological prob-
lems. 1 However, the earliest of these did
not require scientific training or funda-
mental research and, understandably
enough, the infant company supported
neither scientific education nor research.
Not even Bell’s “mechanical assistant,”
Thomas Watson, had any formal scien-
tific training. When the technical staff
expanded during the next few years,
Watson was joined by inventors, not sci-
entists.

To be sure, many telephone problems
of the 1880’s and 1890’s — attenuation and
distortion of telephone signals, crosstalk,
switching, interference from other elec-
trical devices such as street lighting or
electric railways — were caused by elec-
tromagnetic phenomena that were just
receiving scientific explanation. James
Clerk Maxwell’s Treatise on Electricity
and Magnetism had only recently been
published (in 1873), and it had limited
experimental support. (Heinrich Hertz’s
experimental confirmation of electro-
magnetic waves came in 1888.)

The First decisive step towards in-house
research occurred in 1885 when Ham-
mond V. Hayes, the first PhD in the Bell
System (and holder of the second physics
doctorate awarded by Harvard) became
chief of the technical staff. But the en-
gineers on Hayes’s small staff in the 1880’s
were not trained in mathematics and
could not readily apply electromagnetic
theory to the engineering problems they
encountered. Approaching immediate
practical problems by the cut-and-try
approach seemed more promising than
taking staff time out to comprehend and
develop the scientific underpinnings.

Yet even before the turn of the century,
Hayes had hired a handful of university-
trained scientists to work on technical
problems. In 1890 he recruited John
Stone Stone, trained at Johns Hopkins
University in advanced mathematical
theory, to work on sound transmission; in
1897, George Campbell, an MIT-trained
physicist with five years of postdoctoral
study, to clarify the role of the inductive
impedance in telephone communica-
tions, and in 1899, Edwin Colpitts from
Harvard, to study alternating electrical
currents and inductive interference due
to electric trolley cars and power-trans-
mission systems.

Frank Baldwin Jewett (later to become
the first president of Bell Labs) was hired
in 1904 to work under Campbell as a
transmission engineer. Jewett, who was
the first member of the technical staff to
have some close experience with the
atomic physics then being developed, was
teaching physics and electrical engineer-
ing at MIT at the time he was hired.
While in the doctoral program at the
University of Chicago, Jewett had been a
research assistant to A. A. Michelson and
a close friend of Robert Millikan. The
latter, then a young physics instructor,
exposed Jewett to the new discoveries

62

HISTORY OF PHYSICS

being made in electron physics. Jewett’s
association with Millikan would soon
contribute crucially to the beginnings of
basic research within the Bell System.

Thus by 1907 several trained scientists
were working in the company, but pri-
marily as engineers, not as part of an or-
ganized basic-research program.

Spanning the continent

In 1907 Theodore Vail, who had left the
company in a dispute twenty years earlier,
was rehired as President. Two decisions
Vail made then had major impact on the
movement towards establishment of basic
scientific research.

First, he brought together all technical
workers into a single department. The
new engineering department — which
ultimately evolved into the Bell Tele-
phone Laboratories — was established at
463 West Street in New York City as a
division of Bell’s manufacturing arm,
Western Electric. Hayes retired and Vail
appointed John J. Carty to head the new
department. Carty, who at first sight
seems a throwback to an earlier era — he
had joined the company in 1879 as a boy
operator, and had no formal scientific
training — actually proved to be closer to
the new style. He was a research en-
thusiast who had by then made an im-
pressive series of technical contributions
to the art of telephony, including appli-
cation of the two-wire metallic circuit, the
first multiple switchboard, the bridging
bell and the repeating-coil phantom cir-
cuit.

Vail’s second decision was to build a
transcontinental telephone line from New
York to San Francisco, in time for the
1914 Panama-Pacific Exposition. It was
soon recognized, however, that no such
line could be achieved unless a “re-
peater”— a device that could amplify
telephone signals attenuated by dis-

HAMMOND V. HAYES, 1907

tances — could be developed. But to de-
sign a usable amplifier for coast-to-coast
service would require a detailed under-
standing of the new electron physics, a
subject beyond the working knowledge of
anyone then in the company.

Attenuation had become a progres-
sively more obtrusive problem as the
company’s lines lengthened — from ap-
proximately two miles between Boston
and Cambridge in 1876 to 900 miles be-
tween New York and Chicago in 1892, and
then to 2100 miles between New York and
Denver in 1911. As early as 1899,
Campbell had developed a “loading coil,”
which cut energy losses dramatically by
increasing the inductive impedance of the
lines; the New York to Denver line could
not have been built without it. (Michael
Pupin, at Columbia University, also in-
vented the loading coil at this time and
won the patent fight against Campbell.

The company, however, then bought Pu-
pin’s patent, and Campbell went on fur-
ther to develop the loading coil for tele-
phone application.) But to go farther
than Denver it would be necessary to add
an amplifier to the system.

A mechanical amplifier designed by
Herbert Shreeve, based on a vibrating
diaphragm, had been tested as early as
1904. The amplified signal was similar to
the original one but it was typically quite
badly distorted; Shreeve’s repeater
tended to favor some frequencies and
discriminate against others. When used
on lines with loading coils, the signal was
all but destroyed.

Something less sluggish than a vibrat-
ing diaphragm was needed, such as elec-
trified gas particles, or free electrons.
The development of this idea required
knowledge of the most recent electron
physics. Therefore in 1910 Jewett dis-
cussed the problem with his graduate-
school friend Millikan, who later recalled2
that Jewett asked him to recommend
“one or two, or even three, of the best
young men who are taking their doctor-
ates with you and are intimately familiar
with your field. Let us take them into our
laboratory in New York and assign to
them the sole task of developing the
telephone repeater.” Millikan recom-
mended his best graduate student, Harold
Arnold, who in January 1911 joined
Western Electric’s engineering depart-
ment.

The first research branch

Three months later the Bell System
established its first research branch as a
division of this department. Headed by
Colpitts, the new group had as its specific
directive to produce “the highest grade
research laboratory work.” Jewett was
given responsibility for directing research
on the most immediate problem, the re-
peater.

A pattern was developing that would
deepen throughout the following five
decades: The Bell System would support
increasing programs of basic research
within an expanding engineering effort.
In-house research directly pertinent to
communications needs would circumvent
the necessity of buying patents from other
institutions or individuals or, as in the
case of the radio research, would protect
existing Bell patents.

The trend towards more fundamental
studies was reinforced by what was ap-
parently a new, if unwritten, policy: The
directors of research were chosen from
among the scientists who were trained in
the Bell System’s own laboratories. Such
men understood that creative scientists
need freedom to speculate and explore
intellectually and to communicate with
researchers working on similar prob-
lems— even if these were employed out-
side the company. In short, the scientists
required latitude comparable to that
available in academic laboratories. Ac-

THEODORE N. VAIL, 1915

INSTITUTIONS OF PHYSICS

63

GEN. JOHN J. CARTY, WORLD WAR I

tive competition in the larger scientific
community would also be recognized in
time as the most effective means for Bell
to achieve the awareness of scientific
frontiers it deemed necessary to maintain
its market advantage.

The solution to the amplifier problem
began with the triode offered in 1912 to
American Telephone and Telegraph by
Lee De Forest. The triode could amplify
weak signals; however, due to the rela-
tively large telephone currents required,
the gas inside the tube would ionize. As
John Mills recalled, “[the tube] would fill
with blue haze, seem to choke, and then
transmit no further speech until the in-
coming current had been greatly re-
duced.” That problem was eventually
solved by Arnold’s development of a
high-vacuum version of De Forest’s
triode.

The first transcontinental line opened
in time for the Exposition; in January
1915 Alexander Graham Bell in New York
reissued his famous command to his for-
mer assistant in San Francisco: “Mr
Watson — come here — I want you.” To
this Watson replied, “It would take a week
to get there.”

Basic research takes root

In the third stage (1925-35) basic re-
search took firm root in company policy.
In 1925 a new corporation headed by
Jewett — the Bell Telephone Laborato-
ries— took over Western Electric’s engi-
neering department. But the organiza-
tional changes of 1925 did not alter the
new research policy.

Basic research continued to expand and
diversify in the Bell System. The trend
may be illustrated by the work of the
vacuum-tube department, an organiza-

tion that originally had evolved out of the
earlier research on repeaters. By 1930
this department was staffed by almost 200
scientists and co-workers organized in
subgroups focussing on specialized as-
pects of vacuum-tube phenomena. These
included thermionic emission and the
interaction of electrons with solids. Ex-
amples of fundamental research that grew
out of such investigations during the later
1920’s are the well known studies on
thermionic noise by J. B. Johnson and
Harry Nyquist, Harold Black’s important
study of negative feedback, and the fa-
mous experiments by Clinton Davisson
and Lester Germer that provided exper-
imental verification of the wave behavior

of electrons. (It is of interest tha^, Dav-
isson and Germer were not initially aware
of the relafion their experiments had to
quantum mechanics. Instead these ex-
periments were in part an outgrowth of
Arnold’s desire to understand fully the
issues raised in his patent fight with Irving
Langmuir over the development of the
high-vacuum tube.4 5) Among other ex-
amples of fundamental research in this
period was that carried out by Richard
Bozorth on magnetic materials.

In the following decade interactions
increased between researchers at the
Laboratories and those in universities
both here and abroad. The new quantum
physics entered Bell Laboratories re-

JOSEPH A. BECKER AND C. J. CALBICK, 1927

64

HISTORY OF PHYSICS

HAROLD D. ARNOLD, 1931

search and contributed towards still more
intensive focus on fundamental questions.
The quantum theory of solids, developed
between 1926 and 1933 by Wolfgang
Pauli, Werner Heisenberg, Arnold Som-
merfeld, Felix Bloch and others would
create a context for Bell’s innovations of
the subsequent decades in solid-state
physics.

The quantum theory of solids was soon
recognized as relevant to technical studies
at Bell such as thermionic emission,
photoelectricity and conduction. Walter
Brattain and Joseph Becker, for example,
drew upon the classic work of Arnold
Sommerfeld and Lothar Nordheim in
1928 on the electron theory of metals to
compute thermionic emission formu-
las.6

New ideas

The quantum theory entered through
a number of avenues, some of them un-
common for an industrial laboratory of
that period. One of these was Bell’s lively
colloquium series, organized in 1919 “to
review scientific progress by means of
contributed papers and general discus-
sions of current scientific literature.” In
the early years, most of the talks were
given by Bell Labs scientists; during the
1920’s, however, researchers from all over
the world spoke there on recent advances
in physics and chemistry. Prominent
European visitors during the period in-
cluded Sommerfeld, from Munich, who
spoke in 1923 on “Atomic Structure” and
in 1929 on “The Photoelectric Effect in a
Single Atom and in a Metal;” Ernest
Rutherford, from the Cavendish Labo-
ratory, who in 1924 spoke on “Recent
Researches Concerning Atomic Nuclei;”
Erwin Schrodinger, from Zurich and

Berlin, who in 1927 spoke on “The Un-
dulatory Theory of the Electron;” Eugene
Wigner, of Berlin and Princeton, who in
1932 discussed “Applications of Quantum
Mechanics to Chemistry,” and Paul
Ewald, from Stuttgart, who in 1936 spoke
on “Crystal Growth and Crystal Perfec-
tion.”

Distinguished American scientists from
other institutions who delivered colloquia
at Bell in the same period included Robert
Millikan (Cal Tech) in 1925, Robert
Mulliken (New York University) in 1927,
Edward Condon (Princeton) in 1928,
Harold Urey (Columbia University) in
1932, I. I. Rabi (Columbia) in 1933 and
John Van Vleck (Harvard) in 1936. In
December 1933, there was a symposium
on the recently discovered “Positive
Electron.” Speakers included Bell’s Karl
K. Darrow, who gave an historical review,
and Gregory Breit, then at NYU, who
presented P. A. M. Dirac’s theory of holes;
Rabi led the discussion.

Much of the impetus behind Bell’s
colloquium came from Darrow, who had
been on Bell’s staff since 1917. Particu-
larly during the summer months, Darrow
would visit major European and Ameri-
can research centers and attend physi-
cal-society meetings. Scientists often
would accept Darrow’s invitation to visit
Bell Labs and give colloquia there.
During the period, Darrow also helped
transmit new ideas in physics by writing
a semipopular series, “Some Advances in
Contemporary Physics,” for the Bell
System Technical Journal. The topics
included “Waves and Quanta” (1925);
“The Atom-Model” (1925); “Statistical
Theories of Matter, Radiation and Elec-
tricity” (1929), and “The Nucleus” (1933).
The series was widely read and often

evoked strong response; Brattain, for ex-
ample, claims his awareness of Bell Labs
was stimulated by Darrow’s articles
written, as Brattain put it, “in his gor-
geous language.” 7

Individual study and self-education
provided another path of entry for new
ideas at Bell, aided ironically by the De-
pression, which caused a reduction in 1932
of the work week for Bell’s staff from 5
to 4 days. (In 1934 the staff went back to
a 4’/i-day-week and in 1936 to five days.)
In a number of cases the extra time was
devoted to individual study of quantum
physics or to course work at Columbia and
elsewhere. Some study efforts were dis-
seminated more widely in the Laborato-
ries; Brattain, on his return to Bell after
attending Sommerfeld’s lectures on the
electron theory of metals at the 1931
Michigan Summer Symposium, gave a
series of informal lectures on that theo-
ry-

By this time other industrial firms were
also making strides in the application of
research at their institutions. The extent
to which leaders of research saw such ac-
tivity as a common enterprise is illus-
trated by the joint monthly luncheon
meetings of some twenty industrial labo-
ratory leaders including Charles Ketter-
ing of General Motors, Kenneth Mees of
Eastman Kodak, Willis Whitney of Gen-
eral Electric and Jewett of Bell. They
discussed shared problems and issues,
such as organization, personnel, patents
and the relation of industrial research to
economic conditions. Sometimes the
group of “directors of industrial research,”
as they called themselves, would visit each
others’ laboratories. A tradition of indi-
vidual visits to other research laboratories
also evolved in this period.

Industrial researchers were frequently
included in programs of the academic
community. For example, during the late
1920’s and early 1930’s, MIT ran a collo-
quium series within their electrical-engi-
neering department in which members of
various manufacturing, operating and
engineering companies, including Bell
Laboratories, were invited to lecture on
how fundamental science could be applied
to engineering problems. In 1928 Bell’s
Mervin Kelly spoke in this series on
“Thermionic Filaments of Vacuum Tubes
used in Wire Telephony;” in 1936, Bo-
zorth reported on “Recent Research in
Magnetic Alloys.” By the mid-1930’s the
problems, approaches and atmospheres
of fundamental research at Bell Labs were
remarkably similar to those in university
laboratories.

Establishing solid-state research

The fourth stage, the establishment of
basic research in solid-state physics cul-
minating in the development of the
transistor, began in 1936, when Kelly was
appointed director of research. Kelly,
like Arnold and Jewett before him, had
taken his doctorate in physics at Chicago

INSTITUTIONS OF PHYSICS

65

CLINTON S. DAVISSON AND MERVIN J. KELLY, 1951

(where he had worked with Millikan on
the oil-drop experiment), and had for a
period (1928-34) led the vacuum-tube
department. Kelly had become very
much aware of the potential value of an
amplifier without vacuum tubes — which
were large, expensive, fragile, slow, rela-
tively noisy, and often unreliable and
short-lived. He is said to have mani-
fested an interest in the early 1930’s in
developing an amplifier based on the
properties of solid materials.

Some researchers on Bell’s staff were
already exploring the amplification
properties of semiconductors. For ex-
ample, Becker and Brattain were studying
the properties of copper oxide but they
did not fully understand the physical
basis for their observations. Raymond
Sears, who worked closely with Becker
during the 1930’s, recalls:8

"Becker all along felt that there was
something in a copper-oxide rectifier
that ought to have an analogy to the
vacuum tube. There was a nonlinear-
ity of the conduction in the forward and
in the reverse direction. And so Joe
himself would try to imbed a wire mesh
in the oxide layer of copper oxide, in
order to almost try to make a grid, like
in a vacuum tube. I do well remember
that. And Brattain and I would tell
him, ‘Look, that’s not the way to go
about it. You’ve got to understand
how things work.’ ”

Brattain describes9 his original motiva-
tion for attending the Michigan Summer
Symposium in 1931 as his desire to obtain
“a thorough knowledge” of the work
function in thermionic emission and the
photoelectric effect.

Kelly became convinced that the route
to a solid-state amplifier was a deeper
understanding of the basic physics of
solids. By the mid-1930’s he began to
indicate a desire to create a new kind of
research team to be composed of chem-
ists, physicists and metallurgists who
would focus on basic solid-state physics.
This interest, which according to Bozorth
was expressed even earlier by Oliver
Buckley, director of research at Bell from
1933 to 1936, probably motivated Kelly’s
hiring of theoretical physicist William
Shockley in 1936. (In 1952, the year after
Buckley retired as president of the Lab-
oratories, Bell Labs and The American
Physical Society established the Oliver E.
Buckley Prize in solid-state physics, thus
commemorating Buckley’s long-standing
interest in fundamental solid-state
physics research.)

Shockley’s thesis adviser at MIT, John
Slater, was head of one of the two major
US training centers of that period for
young solid-state physicists. The other
was Princeton; several of Eugene Wigner’s
graduate students, e.g., John Bardeen,
Conyers Herring and Frederick Seitz,
became part of the first generation of
physicists to refer to themselves as
“solid-state” physicists. Connections

were close during the early 1930’s between
the physics departments at MIT and
Princeton; Bell’s three leading solid-state
theorists during the mid 1940’s — Shock-
ley, Bardeen and Herring — had known
one another during their graduate-school
days.

At Bell, Shockley first worked on vac-
uum-tube phenomena but soon joined a
new research group under the direction of
Harvey Fletcher, the well known acoustics
researcher who was director of physical
research at that time. This group was
recently described9 by Joseph Burton,
who later became one of its members, as

■ • a group of fairly new people. Wool-
dridge, Townes, Shockley and Nix. All
had been brought up to some degree in
modern solid-state physics.” In this
group, Foster Nix engaged in a series of
studies of phenomena in metals and al-
loys, and interested Shockley in the
order-disorder phenomenon in alloys.
Shockley thus moved closer to basic
solid-state physics, in which he had been
trained at MIT. Dean Wooldridge, who
had joined the Labs in 1936, was at this
time working on the theory of secondary
emission, magnetic sound recording and
television; Charles Townes, who joined in
1939, soon became involved in radar
bombsight research.

Nix recently described10 his impres-
sions of that group: “When Kelly created
this little group of independent people —
there were Shockley and I and Wool-
dridge— under Fletcher, we were told,
‘You do whatever you please; anything
you want to do is all right with me’ . .

Shockley and Nix were central to the
organization in 1936 of an informal study
group approved by Kelly that came to
function as another important avenue for

entry of the quantum theory of solids.
The group — including Shockley, Townes,
Nix and Wooldridge, as well as Brattain
(chiefly working on copper-oxide rectifi-
ers), Alan Holden (whose speciality was
crystals), Addison White (working on di-
electrics), Bozorth (researching magnetic
materials) and Howell Williams (in mag-
netics under Bozorth) — met weekly for
more than four years to discuss the then
recent works on quantum solid-state
physics, including the books by Nevill
Mott and H. Jones, Mott and Ronald
Gurney, Richard Tolman and Linus
Pauling. James Fisk (initially studying
nuclear fission with Shockley) and Burton
(working on photoelectron emission)
joined the study group in 1939.

The transistor

Meanwhile, an advance took place at
Bell’s radio lab in Holmdel, which would
contribute fundamentally to the inven-
tion of the transistor. Several researchers
noticed that some samples of the semi-
conductor silicon were effective detectors
of high-frequency microwaves. One of
the researchers, Russell Ohl, became in-
terested in obtaining pure silicon samples
and involved several of Bell’s metallur-
gists in the problem. During the cooling
of hot silicon ingots, Jack Scaff and Henry
Theurer produced the first silicon p-n
junction; a substantial photovoltaic effect
was produced when the silicon was illu-
minated (this was in 1940).

When Kelly learned of this he recog-
nized that here might be the key to the
solid-state amplifier. Brattain recalls,6
“Becker and I were invited to a con-
ference in Kelly’s office to discuss the
meaning of this phenomenon. We
were presumably the physicists who

66

HISTORY OF PHYSICS

OLIVER E. BUCKLEY, 1952

were supposed to know something
about semiconductors . . . [and] we were
completely flabbergasted at Ohl’s
demonstration. The effect was ap-
parently at least two orders of magni-
tude greater in room light than any-
thing we’d ever seen ... I even thought
my leg maybe was being pulled.”

The beginnings of solid-state physics at
Bell Labs and the first steps towards the
transistor were therefore definitely under
way at the advent of World War II. War
research at Bell and elsewhere led to new
advances, such as resonance techniques,
thermal-neutron scattering and improved
computing methods, which would in the
postwar period contribute in fundamental
ways to solid-state physics. And perhaps
most important to the advancement of
solid-state electronics, a large effort was
invested in development on an expanded
scale of materials with very small quan-
tities of impurities. Silicon and germa-
nium became prototypes for the study of
solid-state physics after the war, in part
because the technology for producing
them had become well developed.

The war also led to nationwide recog-
nition of both industrial and academic
research as a national resource, contrib-
uting to Bell’s growing support of in-
house basic research. President Buckley
expressed his attitude in a letter to The
New York Times of 25 August 1949:
“One sure way to defeat the scientific
spirit is to attempt to direct inquiry
from above. All successful industrial
research directors know this, and have
learned from experience that one thing
a ‘director of research’ must never do is
to direct research, nor can he permit
direction of research by any supervisory
board. Successful research goes in the

direction in which some inquiring mind
finds itself impelled. True, goals are
set, goals of understanding in the case
of fundamental research .... The di-
rector of research does his part by
building teams and seeing that they are
supplied with facilities and given free-
dom to pursue their inquiry. He also
insures for them contacts essential to
their work, but at the same time pro-
tects them from interference or diver-
sion arising from demands of immedi-
ate operating needs . . .”

As to solid-state physics proper, the
long discussions between Buckley and
Kelly on Bell’s basic research during the
late 1930’s and throughout the war years
resulted in formal authorization in Jan-
uary 1945 of the mixed group of re-
searchers that Kelly had envisioned for so
long — the group of physicists, chemists,
physical chemists and metallurgists,
jointly directed to pursue basic research
in solid-state physics. The solid-state
research group was co-headed by the
chemist Stanley Morgan, who had been at
Bell since the mid-1920’s, and the physi-
cist Shockley. The authorization reflects
the vision Kelly had during the 1930’s, of
a unified approach to all solid-state
problems.

Two other basic research groups were
also established at the same time; one,
headed by James Fisk, to pursue funda-
mental studies in electron dynamics, and
another, headed by Wooldridge, devoted
to basic research in physical electronics.
Fisk suggested to Kelly that he invite
Bardeen, by this time recognized as one of
the outstanding solid-state theorists in
the country, to join the new solid-state
group. Bardeen joined in 1945, and in the
following year Herring was hired into the

new physical-electronics group. With the
addition of Bardeen and Herring, Bell
Labs became more than able to hold its
own as a leading research institution, in
theoretical as well as experimental solid-
state physics.

A subgroup of the new solid-state di-
vision under Shockley’s direction — Bar-
deen, Brattain, experimental physicist
Gerald Pearson, physical chemist Robert
Gibney and circuit expert Hiibert
Moore — began to focus on the semicon-
ductors silicon and germanium. In De-
cember 1947, Bardeen and Brattain
demonstrated the first point-contact
transistor and in the following year,
Shockley developed the first junction
transistor. In 1956, Bardeen, Brattain
and Shockley received a Nobel Prize for
invention of the transistor.

First by necessity, then by design

The cycle was now complete: Bell’s
program of basic research, which had
evolved out of technical concerns of an
industry initially generated by one device,
had given birth to another device. And
soon the cycle would expand dramatically,
for the transistor would increase the fi-
nancial base — and the size — of solid-state
physics and begin the age of solid-state
electronics.

A highly successful union had been
achieved in the Bell System of two tradi-
tionally distinct — now proven comple-
mentary— approaches to the physical
world, the more particular approach of
the technical worker and the more ab-
stract approach of the research scientist.
It was a union initiated by necessity and
only later Welded by design.

INSTITUTIONS OF PHYSICS

67

This article summarizes research subsequent-
ly published as three articles: “The Emer-
gence of Basic Research in the Bell Telephone
System 1875-1915, ” Technology and Culture
22, 512 (1981); “The Entry of the Quantum
Theory of Solids into the Bell Telephone Lab-
oratories, 1925-40: A Case-Study of the In-
dustrial Application of Fundamental
Science, ” Minerva 18, 423 (1980); and “The
Discovery of the Point-Contact Transistor, ”
Historical Studies in the Physical Sciences
12, 41 (1981). The research, based on docu-
ments (including notebooks, letters and tech-
nical memoranda) and tape-recorded inter-
views with Bell Laboratories scientists, was
made possible by the cooperation and support
of several institutions, the most prominent
among which are Bell Laboratories and the
Center for History of Physics of the American
Institute of Physics.

References

1. See, for example. A History of Engineering
and Science in the Bell System, The Early
Years ( 1875-1925 ) (M. Fagan, ed.), Bell
Telephone Laboratories, Murray Hill, N.J.
(1975).

2. Autobiography of Robert A. Millikan,
Prentice-Hall, New York (1950), page
117.

3. J. Mills, Bell Tel. Quart. 19, 5 (1940).

4. L. Germer, "The discovery of electron
diffraction,” (unpublished memorandum),
reel 66, Archives for the History of Quan-
tum Physics (available at AIP, New York;
Amer. Philos. Soc., Philadelphia; Niels
Bohr Inst., Copenhagen; University of
California, Berkeley).

5. R. Gehrenbeck, Clinton Davisson, Lester
Germer and the Discovery of Electron

Diffraction, doctoral thesis, University of
Minnesota (1973).

6. W. Brattain, J. Becker, Phys. Rev. 45, 696
(1934).

7. Interview with W. Brattain by A. Holden
and W. J. King, January 1964, Oral History
Collection, AIP Niels Bohr Library, New
York.

8. Interview with R. Sears by L. Hoddeson,
14 July 1975, Oral History Collection, AIP
Niels Bohr Library, New York.

9. Interview with W. Brattain by C. Weiner,
28 May 1974, Oral History Collection, AIP
Niels Bohr Library, New York.

10. Interview with F. Nix by L. Hoddeson, 27
June 1975, Oral History Collection, AIP
Niels Bohr Library, New York.

11. Interview with J. Burton by L. Hoddeson,

22 July 1974, Oral History Collection, AIP
Niels Bohr Library, New York. □

68

HISTORY OF PHYSICS

Paul P. Ewald heads the department of physics
at the Polytechnic Institute of Brooklyn and is
editor of Acta Crystallographica, the international
journal of crystallography. He came to the United
States four years ago from Ireland, where he had
served as professor of mathematical physics at
the Queen’s University in Belfast.

Some personal experiences in

of CRYSTAL

By P. P. Ewald

PHYSICS TODAY / DECEMBER 1953

An article based on Professor Ewald’s ad-
dress as Retiring President of the American
Crystallographic Association at its meeting
in Ann Arbor, Michigan, June 24, 1953.

"XT' -RAY CRYSTALLOGRAPHY, like any good crys-
tallization, grew from a few distinct nuclei. The
first nucleus was the Laue-Friedrich-Knipping experi-
ment in Munich. Hardly had the news of this new
effect been given at the spring 1912 meeting of the
Bavarian Academy of Science and found its way into
the papers, before a second nucleation was induced in
England. While Laue had explained the effect as one of
diffraction of very short light waves by the regular
lattice arrangement of scattering atoms, W. L. Bragg
concluded from the shape of the Laue spots that they
should be explained as an effect of reflection of waves on
the internal atomic planes, an idea that led him at once
to what is now known as Bragg’s Law. Thus it was the
focusing property which gave the first clue to the Bragg
version of the phenomenon, as published in the Proceed-
ings of the Cambridge Philosophical Society in Novem-
ber 1912.

Soon after this W. H. Bragg applied this principle in
the construction of the x-ray spectrometer, an instru-
ment which led to the fundamental discovery of the K
and L series of characteristic line spectra as distinct
from the continuous “white” spectrum of the general
Bremsstrahlung. With this discovery the wide field of
x-ray spectroscopy was opened up precisely in time to
give convincing support to the Bohr theory” of the atom
in its first infancy and subsequently throughout the
stages of increasing refinement and complexity. The
second wide field opened up by W. H. Bragg’s discovery
was x-ray crystal analysis, for which the characteristic
wavelengths provided the yardstick for measuring the
distances between atoms or atomic net planes in a
crystal. The use of this yardstick was, however, only
obtainable by first determining a crystal structure with-
out its application. This was achieved by W. L. Bragg
by comparing the Laue pictures of NaCl, KC1, KBr,
and KI; the changes produced in replacing a lighter

atom by a heavier one of greater reflecting power led to
the confirmation of the “spatial chessboard” structure
which had been postulated for these salts by Barlow
and Pope. Once the relative arrangement of the atoms
was known, the absolute scale of their distances fol-
lowed from the density of the crystal.

What exciting years were these last pre-war years
1912 and 1913. They belong to those periods of erup-
tive development that occur when an entirely new
impact hits and unites fields of science which for many
years had not yielded to the most strenuous external
pressures. This had been the case with x-rays prior to
1912, with optical spectroscopy and with the interpreta-
tion of the first quantum phenomena in the theories of
radiation and of the photo-electric effect. In these same
years a revival of interest in the theory of the solid state
took place; in Born-Karman’s paper on specific heat
(1912) the first application of quantization to the lattice
model of solids was made, and shortly after that, in
1915, appeared Born’s Dynamik der Kris tall git ter which
marks the nucleation of the modern theory of solids.
Immediate as the impact of the new discoveries was on
physics, it was a delayed one for chemistry. The fact
that in simple inorganic salts the concept of a molecule
should no longer hold did not please the chemists.
Ephraim’s book on inorganic chemistry was, as far as
I am aware, the first textbook fully to accept this fact,
but it did not appear until 1921. Progress in x-ray
diffraction came from many European countries in those
early years. Maurice de Broglie in Paris was quick in
developing his own spectroscopic methods and in train-
ing co-workers like Trillat and Thibaut. Some members
of this audience may remember the unique setup of his
laboratory in his private hotel in the rue Lord Byron
where cables for the current came in by holes cut in
the Gobelins adorning the walls. In Holland Lorentz
developed the Lorentz-factor in his lectures and Debye,

INSTITUTIONS OF PHYSICS

69

the international

coordination

DIFFRACTOMETRY

at that time in Utrecht, ventured to tackle the theory
of diffraction by a lattice in thermal vibration — a prob-
lem which appeared superhuman to anyone but a
Debye. In England Moseley made the first systematic
survey of the K- and L-series throughout the periodic
system and Darwin discussed the absolute intensity of
x-ray reflection by setting up the first dynamical theory
far ahead of all others; in order to account for the
difference between the theoretically expected, and the
observed intensities, he developed the idea of the mosaic
crystal which proved indispensable for all later work.
The crystallographer G. Wulff in Russia showed the
advantages of crystallographic projection techniques;
Nishikawa obtained the first fibre diagrams and Terada,
also in Tokyo, was the first to observe the sudden ap-
pearance and disappearance of the diffracted spectra
on the fluorescent screen. Remember that all this
happened at a time when the identity of the Bjragg
reflection and the Laue diffraction theories was not yet
generally understood.

It is hard nowadays, especially for the younger
among you who have been taught x-ray diffraction in a
well organized university course, to imagine how crystal
analysis then appeared to those engaged in it. It may
be illustrated by a post card I received from W. L.
Bragg on which he wrote that he had measured the
spectra of pyrites and had been trying to obtain the
structure. “But it is terribly complicated” , he wrote. It
was the first example of a cubic crystal in which the
trigonal axes do not intersect.

f I ' HE WAR of 1914-18 brought not only the inter-
A ruption of international relations, it even brought
the actual x-ray diffraction studies very nearly to a
standstill. The application of these studies to chemical
and technical problems had not yet been discovered.
Only one advance of great importance was made in
1917, and that independently in Gottingen and in
Schenectady by Debye and Scherer and by A. W. Hull,
respectively. While all previous measurements required
fairly large well-formed single crystals, which were not
always easy to obtain, the powder method was ap-
plicable to practically all solid substances. I first heard
of this method from the crystallographer A. Johnsen,
then professor in Kiel, and keeper of a fine collection
of minerals. His words, which I remember well, are
significant for the enthusiasm with which the powder
method was acclaimed: Who would still want to take
single crystal pictures, painstakingly adjusted and hard
to index? We just powder our crystals in a mortar and

get the pow'der lines to fit into a quadratic form and
that gives us all the information.

In the period after 1918 the retarded development
flared up afresh. The two Bragg schools, at the Royal
Institution and in Manchester, were the leading centers
for structure analysis and for the training of the next
generation of physicists in this art. They were also an
international meeting ground of crystallographers. The
spectrometer remained for a long time the main instru-
ment. Apart from giving a direct indication of the
strength of reflection, it offered the great convenience of
showing exactly from what plane the reflection came, an
advantage that was lost in the rotation diagrams of
Polanyi (1921) and only regained in the Weissenberg
x-ray goniometer method (1924). The deciphering of
the experimental data was achieved by frontal assault
in each case. A “normal” decline of intensity with in-
creasing order of reflection was established by W. H.
Bragg and the deviations from the normal sequence
were attributed to the halvings or similar subdivisions of
the sets of reflecting planes and later to the structure
factor. The usefulness of space group theory in provid-
ing a framework for the atomic positions was stressed
by Niggli in his book (1919), but given the practical
test by Wyckoff, together with his numerous co-wmrkers,
in determining a great number of structures with the
help of his Analytical Expression of the Results of the
Theory of Space Groups which appeared in 1922. The
first English adaptation of the theory of space groups
followed in 1924 (Astbury and Yardley).

About the same time the first books on the new
subject appeared. The book by the Braggs, X-Rays and
Crystal Structure, had already been published in 1915;
it gave mainly a coordinated account of their own
investigations and is still a fundamental book, unique for
the simplicity of its reasoning and the beauty of its
style. It gave the direction to the English school of
x-ray workers, but it was never meant, at the early date
of its publication, to present more than the line of
thought that had achieved the great first results. It was
often reprinted but never expanded or revised.

My own book, Kristalle und Rontgenstrahlen (1923),
represented the continental point of view and aimed at
integration of the advances in the methods of x-ray
diffraction and at discussing the implications of the
results. It was sold out in two years and I never pre-
pared a second edition, partly because the subject was
growing so rapidly, but mainly because the two editions
of the chapter I wrote for the Handbuch der Physik
(1926 and 1933) gave a more succinct and modern
presentation of the same matter.

70

HISTORY OF PHYSICS

Similar monographs on the subject were written in
France by Ch. Mauguin (1924) and in the U.S.A. by
Wyckoff (The Structure of Crystals, 1924). Together
these three early books document in detail the advances
made up to about 1923 regarding the methods of pro-
ducing and indexing diffraction photographs and of
using the structure factor for obtaining the atomic ar-
rangement. Significantly neither Wyckoff’s nor my book
contains a main chapter on the intensity of diffraction;
in spite of Lorentz’, Darwin’s, and Debye’s work too
little was known about it. Mauguin deals more fully
with intensity.

1V/T EANWHILE the x-ray crystallographers were be-
coming more ambitious. The first structures that
had been determined, like NaCl, diamond, zinc blende
and wurtzite, had been without a parameter; the atoms
could not be moved away from the intersection of sym-
metry elements in the cell without admitting too many
atoms to the cell. In pyrites and calcite, structures
with one parameter had been solved by discussing the
intensity sequence among the various orders of reflec-
tion of a face. It was still fairly easy to extend the
methods of discussion to the case of two, and, in rare
cases, of three parameters. But you could not set out to
determine the structure of any given crystal, because in
most cases it was likely to contain a large number of
parameters. The purely optical principles of discussion
then broke down. At this stage the idea of fixed atomic
radii was introduced by W. L. Bragg and his school and
eagerly expanded and modified by V. M. Goldschmidt
and others. Nowadays it is a valid and much employed
principle which is firmly based on a large body of
experience. It appeared a risky principle in the mid-
twenties and one would have liked first firmly to estab-
lish it on a large number of structures which had been
determined without its use. This gave a special mean-
ing to the collection of structure data which C. Her-
mann and I assembled as Vol. 1 of the Strukturberichte.
In reporting the structure determinations we tried here
to separate clearly the optical arguments, which seemed
safe, from any doubtful additional hypotheses. Wyckoff
followed the same line in his critical surveys of struc-
tures which were published in 1924, 1931, and 1935.
This purist tendency has been dropped deliberately from
the recent revival of the Strukturberichte , the Structure
Reports.

In spite of auxiliary assumptions derived from atomic
radii and structural chemistry the full structural analysis
of crystals containing three or more parameters re-
mained at best a hazardous undertaking. All problems
seemed to end up in a sigh: if only we had a reliable
means of measuring and evaluating intensities and of
deriving from them the structure factors! It is true that
in 1914 Darwin had given two expressions for the in-
tensity of an x-ray reflected by the external face of a
crystal, assuming either a perfect or a mosaic crystal.
These expressions gave widely different values, and the
measured intensities did not seem to fit either assump-
tion too well. Besides, Darwin’s papers were not well

written and were not properly understood. His restric-
tion to the specular reflection from the net planes gave
no indication as to what became of the cross-grating
spectra which each of these planes would give owing
to its own atomic periodicity. This was one of the
reasons which prevented me from appreciating Darwin’s
work, and it was only after having set up my own
dynamical theory of x-ray diffraction that I discovered
that some of my results for a perfect crystal were
identical with those of Darwin. Experimentally Bragg
and James and Bosanquet showed in 1921 that the in-
tensity of reflection depends largely on the treatment
given to the reflecting surface of the crystal, such as
grinding, polishing, etching.

By 1925 it had become apparent that the whole
future of x-ray crystal analysis was at stake unless a
solution to the intensity problem could be found. I
learned that Wyckoff was coming to Europe and it
occurred to me that this would offer an excellent occa-
sion for having a joint discussion of all those who had
worked on the intensity problem. After some cor-
respondence I found a date in August, 1925, which was
acceptable to nearly the whole group of experts and I
arranged for five days of discussion at my mother’s
house in the country at Holzhausen on the Ammersee,
some 25 miles from Munich. The little local inn was
rented, a blackboard was borrowed from the nearest
country school and a few boxes of cigars placed on the
table in my mother’s big studio (she was a painter).
Then the exciting moments came of meeting my col-
leagues at the nearest railway station at which they,
fortunately, all arrived on schedule. Remember that by
1925 the international relations had not yet been re-
sumed on any large scale and that this was for most
of us the first post-war meeting of an international
character. Those present were, if I remember cor-
rectly, W. L. Bragg, Darwin and James from England;
Wyckoff from U.S.A. ; Brillouin from France; Fokker
from Holland; Waller from Sweden; Laue, Mark, Ott,
Herzfeld, and myself from Germany. Occasional visitors
and participants were Debye and Fajans. Waller had
just published his dissertation ; the first part of this was
a review and extension of the dynamical theory and the
second an extension of Debye’s work on the temperature
factor. It was a very learned paper and required many
years of development to be fully evaluated in its impli-
cations for the discussion of experimental results.

I think all of us enjoyed these full days of intense
discussion in which Darwin finally got so entangled be-
tween his own papers of 1914 and 1922 that he promised
to restate them and where Bragg declared emphatically
at the end of one session: I will not be satisfied unless I
can determine a structure with 19 parameters! This
seemed utterly fantastic at that time, and yet, two or
three years later, he was tackling the silicates and
polytungstanates and was just about as far as he had
wished. The Holzhausen conference was an important
event in the history of x-ray crystallography. It co-
ordinated at a critical time the various approaches,
experimental and theoretical, British and Continental,

INSTITUTIONS OF PHYSICS

71

i.e. reflection versus diffraction. It further made scien-
tists meet after the war, many of them for the first
time, and laid, I am happy to say, the foundations for a
lasting personal friendship and respect. In doing so, it
also paved the way for two of the future international
enterprises in crystallography, the Strukturberichte and
the International Tables. It stimulated experimental and
theoretical work in the problems discussed at the meet-
ing as is shown by a number of papers in the subsequent
years. But the credit for overcoming the formidable
deadlock of the intensity problem goes to W. L. Bragg
who returned to Manchester to tackle it in a most
systematic and realistic way. He first established a
standard of intensity in the 400 reflections of a properly
prepared rock salt face; together with James and
Darwin he restated the results of the latter’s theory in
a Phil. Mag. paper of 1926; James, with Miss Firth,
Brindley, and others, made a thorough experimental
study of the temperature effect using high and low
temperatures; Waller came to Manchester to help on
the theoretical side. As a result of fundamental im-
portance for all parts of physics the first direct
confirmation of the zero point energy of an oscillator,
here the crystal proper vibrations, was obtained.
Hartree, then also at Manchester, tackled the remaining
unknown intensity factor, the atomic factor, first on the
Bohr orbit atomic model, and, after the advent of wave-
mechanics in 1926, by the method of self-consistent
field. Bragg, in 1927, reported on the atomic factor
derived from the Thomas statistical model of the atom.

This may give an idea of the concerted effort wrhich
finally overcame the deadlock.

T> Y THIS TIME advantage was taken, also by the
A-' English workers, of the theory of space groups.
Bernal came to see me in Stuttgart in 1925 carrying
along a voluminous manuscript in which he had de-
rived the 230 space groups in his own way. The prob-
lem was how to publish this work. As happened not
infrequently to Bernal, the manuscript was interspersed
with folding tables densely covered with symbols in
order to accommodate all information on them. He
had devised his own symbols for the space groups and
it was all Greek to me. I well remember the three of us,
Bernal, myself, and Carl Hermann sitting alongside on
a sofa and the maps being unfolded on my knees. It
took Hermann a split second to understand the tables,
including the strange terminology, and to suggest various
points of rearrangement of the tables in order better
to bring out some of the subgroup relations which
Bernal’s arrangement did not show'. The battle between
them was fought out on my knees, and it took close to
an hour to go through the tables.

Several new books had been published or were being
written, such as Mark’s book Die V erwendung der
Rontgenstrahlen in Chemie und Technik (1926), Mark
and Rosbaud’s Space Group Tables, my own Handbuch
article (1926), and a book by Schleede and Schneider
which was being planned. Besides, the older books
needed new editions by 1928. It was a matter of some

concern to me, and I am sure to the other authors also,
how to get around the dilemma either of having to in-
clude detailed tables and illustrations of the 230 pages
groups, or of writing a book that lacked practical
value for the actual determination of crystal structures.
Besides, there were proposals by Rinne and Schiebold,
by Hermann, by Mauguin, and others for changing
the nomenclature of the space groups so as to make
it more descriptive than the Schoenflies symbols. A
multiplicity of symbols for the same space group was
going to create considerable confusion in an already
sufficiently complex subject. The only way I saw out
of this confused situation was the preparation of a set
of impersonal tables containing a complete and standard
description of each space group, a work to which each
author could refer in his own textbook and from which
he could pick examples on which to discuss the ideas
of space group theory, without being obliged to bring
a complete set of tables. I discussed this idea with
Bernal and Mrs. Lonsdale at the occasion of a meeting
of the Faraday Society in London, 1929, and together
we laid it before Sir William Bragg who gave us every
encouragement and promise of help and convened a
meeting of a large group of crystallographers gathered
for the Faraday Society, where this plan and others
were discussed. Bernal and I undertook to prepare a
detailed syllabus of such tables. We hit upon all kinds
of difficulties, partly because decisions had to be taken
concerning the symmetry axes of the second kind, the
fixing of origins, the graphical representation of sym-
metry elements and of equivalent points, etc., and
partly for reasons of a more personal nature because
people in different laboratories and countries had be-
come used to symbols and drawings which did not
please those accustomed to others. A conference was
the only way to thrash out these points, and, again
taking advantage of a European trip of Wyckoff, Bernal
and I prepared a meeting for July 1930. On the invita-
tion of Niggli it was held at his institute. I took the
chair at the four-day meeting, and we worked quite
hard all the time. Those present were Wyckoff from the
U.S.A., Bernal, Astbury and Mrs. Lonsdale from Eng-
land, Mauguin from France, Niggli and Brandenberger
from Switzerland, Kolkmeijer from Holland and myself,
Hermann, Schiebold and Schneider from Germany.
The questionnaire Bernal and I had circulated together
with the invitation gave a lead to the discussions and
some of the points were quickly settled. Hermann’s
notation was recognized to offer great advantages, and
some simplifications which Mauguin proposed were ac-
cepted; Schiebold, somewhat reluctantly, refrained from
pressing for the acceptance of his system. A rather
lengthy skirmish took place over the graphical repre-
sentations. The English were accustomed to the Ast-
bury-Yardley diagrams, Niggli to those in his book to
which most others were not partial. Mauguin circulated
a neat set of cards which he used in his course showing
the cell and a group of equivalent atoms for each space
group but leaving out the indication of symmetry ele-

72

HISTORY OF PHYSICS

ments. It was finally agreed to give two figures for each
space group, one showing the equivalent points in
Mauguin’s way, the other the symmetry elements in a
modified form of Niggli’s representation. Preference for
taking the origin at a center of symmetry whenever
possible, and of using rotation-inversion rather than
rotation-reflection axes was soon agreed upon. Wyckoff’s
symbols for special positions were adopted and so was
the product form for the structure factors, as given in
Mrs. Lonsdale’s Tables. It was further agreed to list the
sub-groups for every group.

The discussion on the third day was on the second
volume which deals with mathematical and physical
tables. The details of the tables of trigonometrical
functions were laid out in a form convenient for the
calculation of structure factors; other trigonometric
tables, useful for the calculation of absorption and
other corrections were planned. The listing of absorp-
tion coefficients and of atomic factors, and many other
details, were discussed along with the distribution of
the work between the laboratories. It was also agreed
to offer the Tables for publication to the publisher of
Niggli’s book.

In the preface of the Ititernationale Tabellen you
will find details of the work supplied by the various
groups, and a list of the Learned Societies whose gen-
erous subsidies made possible the publication of the
work at a very reasonable price. The Tables appeared
in 1935 and it has always made me happy that they
were universally accepted and fulfilled the hopes in
which they were conceived.

THE NEXT international enterprise for which I
worked was the foundation of an international
organization of crystallographers. It began in 1944 when
I was asked by the X-Ray Analysis Group to give an
evening lecture at the March meeting in Oxford. The
second part of this talk was the plea for the formation
of an International Union of Crystallography. This plea
was published in Nature (154, 628, 1944). It sets out,
as the main task of the Union:

(1) the publication of an international journal of
crystallography ;

(2) the establishment of archives for the storing of
scientific results which would be too costly to publish
in full;

(3) the abstracting, summarizing, and recording of
crystallographic work, in particular in connection with
the planned general scientific abstracting scheme;

(4) the preparation of a second edition of the In-
ternational Tables, and their public ownership;

(5) the preparation or coordination of analytical
tables for identifying crystals (Barker index, card index
of powder lines) ;

(6) the representation of crystallography in the sys-
tem of other international scientific unions.

The ball set rolling in Oxford w'as played in great
style by W. L. Bragg who arranged an international
congress of crystallographers in London in 1946. This
was actually the second international congress, the first
having been held in 1934 under the auspices of the

Union of Physics when Sir William Bragg was its presi-
dent. It is unnecessary to recall the events in London
which ended with the resolutions to found a Union,
preferably an independent Union of Crystallography
and, if this were not accepted by the International
Council of Scientific Unions (ICSU), to form a group
within the Union of Physics; further to start at once
with the preparations for an international crystallo-
graphic journal, for the resumption of Strukturberichte
in a new form, and for a new edition of Internationale
Tabellen. The discussions of the committees nominated
for these tasks began without delay while the foreign
visitors were still about. In fact, the Russian delega-
tion which arrived a day after the congress had closed,
was just in time to take part in the discussions on the
journal which took place a few days later in Cambridge.
It is thanks to them that Acta Crystallo graphica carries
its name.

The actual birthday of the International Union of
Crystallography was the hot 3rd of August, 1948, at the
Union’s first Assembly at Harvard. It was the culmina-
tion of a long sustained effort of preparations, including
ocean crossings and oceans of correspondence on the
part of a great number of crystallographers. Everything
was set for the Union to crystallize out at this meeting.
Then an unforeseen inhibition occurred. The provisional
executive committee had proposed to change the first
draft of the Statutes of the Union in some points re-
garding the voting power of the delegates. The new
formulation had to be accepted before the Statutes
could be passed en bloc. So the changes had to be
voted on, especially since there were some objections.
Somebody raised the question: on what voting power
is this going to be decided? Neither the first draft nor
its amendment were binding, since neither had been
accepted. Arguments for voting on the old or the new
scheme went on in a freakish way. Finally the heat, I
guess, must have concentrated the solute sufficiently, so
that the inhibition was overcome and the Union at last
crystallized out by the adoption of the revised statutes
en bloc.

TOOKING BACK to 1946 and 1948 we may ask
-■—4 ourselves whether the foundation of the Inter-
national Union of Crystallography was worth while.
To answer this question we have not only to study
what the Union has achieved, but also where we would
be without it. Its main achievements are the journal
Acta Crystallo graphica, the two, and soon four, volumes
of Structure Reports, and the first volume of the new
version of International Tables; besides, there are the
two international Congresses and Assemblies — Harvard
1948 and Stockholm 1951— to which the third As-
sembly in Paris 1954 will be added next year. Further-
more, there is active work going on by correspondence in
the commissions of the Union, as on Powder Data, on
Apparatus and Standardization, and on Nomenclature.
Within the system of International Scientific Unions the
Union of Crystallography belongs to the small Unions,
small by the number of adhering countries, by its

INSTITUTIONS OF PHYSICS

73

financial demands, and by the limited importance of its
international program which is not as vital in crystal-
lography as it is in astronomy, geodesy and geophysics,
or radio science, and not as extended as in chemistry
and biological sciences. But as a small Union it has
earned respect and acknowledgment by the determined
effort to achieve internationally important results in
the field of publication and standardization. Had the
Union failed to materialize it is most likely that by
now we would have three full-fledged crystallographic
journals, in the States, in England, and in Germany.
Each of these journals would be indispensable because
each would contain important papers. There would be
three editorial, and, worse, three publishers’ policies
regarding the scope and length of the papers, the
yearly published volume, and the price. It is unlikely
that private publishers would have received the generous
subsidies on which Acta Crystallographica was started.
In the first five years Acta has received altogether
$17 400 from Unesco and from industry. These sub-
sidies have helped over the first few years which are a
critical time for a journal. Thanks to this help we have
been able to accommodate an ever increasing influx of
papers. The number of pages published has risen in
the last three years by 78 percent, the production cost
per page by 7.8 percent. The number of subscribers has
been increasing steadily, at a rate of about SO more
subscriptions every year, and this is a healthy sign.
Unfortunately, however, this rate is far too slow to
offset the increase in cost of production. It means that
at present Acta is adding to the “red” in the Union’s
books a deficit of about $10 000 per year. We are thus
still in the midst of the teething troubles of our five-
year-old baby.

It is not unnatural that this should happen. When
the journal was started, it was done on the under-
standing that the price per volume be $10 and that
the balance between production cost and sales be met by
the subsidies. The $10 price was maintained for the
first three volumes, then at the Stockholm Assembly
the price was raised by 50 percent to $15, but mean-
while the volume had increased by 200 percent against
the first volume. Now you might ask: is it necessary
to publish that many papers? A moment’s considera-
tion will show you that it is a natural development.
An increasing number of people trained in crystal
analysis produces more and better papers every year;
the advances in x-ray diffraction technique alone, and
again in computational technique, allow an increased
output of structure determinations, and the ever
closer connection with chemical, biochemical, metal-
lurgical, and physical investigation presents the diffrac-
tionist with problems of considerable interest in nearly
overwhelming numbers. If the journal of the Interna-
tional Union of Crystallography is to tie together all this
diverse diffraction work and be the forum for its
adequate discussion, then we cannot afford to turn
down good manuscripts because we are getting too
many of them for a strictly limited volume. For the
last few weeks I have felt very unhappy in following

this course after having received strict orders from the
Executive Committee at our Paris meeting not to ex-
ceed last year’s volume.

What then can be done with Acta? We have now
some 1100 subscribers, that is double the highest
figure ever obtained for the Zeitschrijt fur Kristal-
lographie. This number is considerably below1 the satura-
tion value, which I estimate at 2000. There are many
university and industrial laboratories without Acta, in
spite of their interest in the solid state. Many big
establishments take only a single copy in spite of
demand in different localities. There are also many
among you who do not yet take advantage of the
reduced price at which you can get your own copy to
study at your leisure at home. The Physical Review is
received by nearly every one of the 10 000 members of
the APS and he pays for it in his membership fee. If
we were similarly to arrange a general distribution of
Acta to the 700 ACA members, of whom about 100
already take Acta at the reduced rate of $9, this
would bring in one-half of the yearly deficit. But so far
the ACA Council has not taken to this proposal.

There are two ways out of this rather desperate
situation: One is to collect further subsidies, preferably
guaranteed over a number of years, and to continue
running the journal at a loss. The private subscriber
may like this proposal because he is getting the benefit
of the subsidy. But it puts the journal on an unsafe
basis and endangers its financial independence. The
other way is to increase the price of subscription so that
the journal is self-sustaining. With the present volume
and number of subscribers this point would be reached
by raising the subscription rate from $15 ($9) to $24
($15). Some income could also be gained by carrying
advertisements, but this is not considerable. A page
charge, while acceptable in the U.S.A., appears unac-
ceptable to the European scientists. Further income will
be necessary later for following the natural develop-
ment, i.e. increasing the volume beyond the present 870
pages; this will have to be met by a further substantial
increase in the number of subscribers.

I think it is important to explain this situation to a
group such as is assembled here. We should not take
the existence of scientific journals for granted. Each
one of us should fight for their existence and make
sacrifices, not only by saving space in his own publica-
tions by the utmost condensation, but also by sub-
scribing and getting others to subscribe. Only by a
deliberate and concerted effort can Acta, and also the
two other publications of the International Union of
Crystallography be brought over the inevitable dif-
ficulties of the first ten years. The gain these publica-
tions bring to the large fellowship of crystallographers
all over the w'orld seems to me to justify the existence
of the Union and to make it worth while not to relax
in sustaining its activities. We may, I think, be proud
of what has been achieved so far and it seems un-
thinkable that the International Union of Crystal-
lography should not be able to keep pace with the
development of crystallography itself.

74

HISTORY OF PHYSICS

the founding
of the

AMERICAN INSTITUTE OF PHYSICS

The following talk was presented at the Banquet of the American
Institute of Physics and the Member Societies in Chicago on Octo-
ber 25, 1951. Senator Brien McMahon, chairman of the Joint Con-
gressional Committee on Atomic Energy, also addressed the gathering.

By Karl T. Compton PHYSICS TODAY / FEBRUARY 1952

FIRST may I add my greeting to Senator McMahon,
and add my appreciation of his willingness to meet
with us tonight. He and we have a strong bond in
common. We physicists have been largely responsible
for creating the activity for whose wise handling in
the national interest he has so great a responsibility.
And may I say, on the basis of several opportunities to
see him in the discharge of these responsibilities, that
we are very fortunate in having this aspect of our
common interest in the hands of a man who has shown
such real understanding of the basic conditions for
scientific development and for advantageous applica-
tion of the great potentialities of atomic energy.

Next let me try to give a bit of historical perspec-
tive to my reminiscences about the formation of the
American Institute of Physics. This is its 20th an-
niversary, and 1931 wTas a milestone. There was another
milestone, definite in character though not sharply
defined as to date, about twenty years before that.
This was the time when it was beginning to be re-
spectable and effective for physicists to stay in the
United States for their postgraduate study instead of
going to Europe. During the ensuing two decades,
physics grew rapidly, being part and parcel of the new
development of postgraduate schools in this country,
being stimulated by the teamwork of groups assembled
for tackling some of the technical problems of World
War I, and being greatly advanced by the program
of National Research Fellowships supported by the
Rockefeller Foundation shortly after the war.

But, in spite of this rapid development of physics
during the “teens” and the “twenties”, the general
public was not very aware of this growing profession,

soon destined to be of such earth-shaking significance,
in both the figurative and the literal sense. For ex-
ample, in the edition of Webster’s New International
Dictionary, published four years after the establish-
ment of the American Institute of Physics, the pre-
ferred definition of a physicist was “One versed in
medicine”. The average citizen would associate the
words physics and physical scientist with certain in-
testinal disorders or with gymnasium drill. In certain
states, where some kind of registration of employees
was required, the profession of physics was not rec-
ognized, and physicists had to register as either engi-
neers or chemists, which some of them felt to be
rather humiliating.

With this background of vigorous growth of this
young, and then inadequately recognized, profession,
let me proceed with the story of the organization of the
American Institute of Physics.

WHEN Dr. Klopsteg asked me some months ago
to give some reminiscences covering the es-
tablishment of the American Institute of Physics, I at
first hesitated because of an impairment of my vocal
apparatus. But I accepted because this Institute rep-
resents a momentous achievement in the development
of organized physics in this country; and also because
I owe a very great personal debt to the American
Physical Society and the other societies associated
with it in the Institute.

In 1909, just sixteen years after the establishment
of The Physical Review, I submitted for publication
my first piece of research, which was my master’s
thesis at the college of Wooster in Ohio. The college

75

INSTITUTIONS OF PHYSICS

Karl T. Compton, chairman of the cor-
poration of the Massachusetts Institute
of Technology, served as the AIP’s first
chairman from 1931 to 1936. A past pres-
ident of the American Physical Society,
I)r. Compton has held numerous posi-
tions of importance in industry, the
government, educational institutions and
foundations, and professional organiza-
tions.

at that time did not subscribe to The Physical Re-
view, and I had no background of information re-
garding the proper form and length of a scientific
article for such a journal. I consequently shipped the
manuscript of my thesis on to Professor Merritt, who
was then editor of The Physical Review — without
realizing that its two hundred typewritten pages and
numerous photographs would have constituted an ar-
ticle many times too long for publication, even in
those days when editorial policy was far less strict
than at present. In spite of the inappropriate length
and character of this manuscript, I received from
Professor Merritt a long letter giving detailed sug-
gestions for rewriting the material. I tried a second
time, and again Professor Merritt wrote back, saying
that he felt the material had now been condensed
to the point at which certain parts were not clear and
again making suggestions for another revision; and
this time the article was published.

I have often thought that this extraordinary help
given by a great physicist to an unknown student in a
small college, and involving on his part a great deal of
work, was a splendid illustration of the helpful con-
cern of the pioneers in scientific education in this
country to encourage the development of their suc-
cessors. Certainly, for me, it was both an inspiration
and a lesson. Since that time I have always feh that
any service which I could render to The Physical Re-
view and to the profession of physics was an obliga-
tion as well as a pleasure.

During the decade following World War I, the rapid
increase of research in the field of physics led to fi-
nancial difficulties for The Physical Review.

To tackle the financial problem, the Council of the
American Physical Society in the latter half of the
1920’s appointed a Committee on the Financial Status
of The Physical Review. The problem confronting
this committee, of which I was a member, was not
only financial, but also involved the great delay in
publication caused by the accumulation of manuscripts,
which the Society could not afford to publish promptly.
To meet this situation, several steps were taken, in-
cluding: a more rigid editorial policy, an increase in
the annual dues of members, and introduction of the
“per page charge to authors”.

When this “per page charge” plan was put into ef-
fect, it was quickly accepted by some organizations
but not by others. Very generously at this point our
fellow member, Dr. Alfred L. Loomis, stepped into
the breach and undertook for an introductory period
personally to take care of the “per page charge” for
institutions which reported themselves unable to meet
the charge. Gradually, however, the plan gained gen-
eral acceptance and is now a regular part of the finan-
cial basis of our physics publications, and has subse-
quently been adopted by other scientific organizations.

T'X URING that same period, in the late 1920’s, an-
other problem presented itself to the American
Physical Society. This was the emergence of groups of
physicists who felt that the main current of interest in
the American Physical Society was not meeting their
particular professional requirements. These groups un-
dertook to establish new societies and new publica-
tions devoted to their important and special interests.
Consequently, the American Physical Society was con-
cerned over the centrifugal tendency to separate the
basic science of physics into a number of independent
groups. Very naturally, each of these groups had its
own financial problems of publication.

My own attention was first drawn to the possibility
of a better coordination of the various physics groups
by a conversation which I had with Mr. William Buf-
fum who was at that time the executive officer of the
Chemical Foundation. I had gone to him for financial
help for The Physical Review. He told me that he
had also been approached by various other physics
groups and it was his impression that the whole pro-
fession of physics was running away in different direc-
tions by independent groups without much coordina-
tion. He said that the Chemical Foundation did not
feel that it would be a wise expenditure of its funds
to support the separate groups, but that if some way
could be found to bring them together in some sort
of coordinated program, then he leit that the Found-
dation would be very much interested in helping to
establish such a program.

From this point on, my recollection of events is
very much amplified by excerpts from the records of

76

HISTORY OF PHYSICS

the Council of the American Physical Society, which
Karl K. Darrow very kindly dug out for me from the
record books.

The first mention in the minutes of the Council of
the American Physical Society of some official move
toward coordination of the various activities in physics
was taken on a motion of Professor G. W. Stewart at
the Chicago meeting on 29 November 1929. On his
motion the Council voted that a committee of three
be appointed “with the President of the Society (H. G.
Gale) as Chairman, which shall, after conference with
the officers of the Optical Society of America, the
Acoustical Society of America, and any other physics
societies, recommend a plan of merger of these so-
cieties with the American Physical Society, and which
shall present a preliminary report for discussion by
the Council at the Des Moines meeting,” in the fol-
lowing December. This committee consisted, in addi-
tion to President Gale, of G. W. Stewart, H. E. Ives,
and D. C. Miller.

From this time on, until the actual establishment of
the American Institute of Physics two years later, the
problem of coordination of the various physics groups
was a matter of discussion and report at every Coun-
cil meeting.

The Council, at its April 1930 meeting in Washing-
ton, appointed a Committee on Applied Physics under
the chairmanship of Dr. Paul D. Foote and compris-
ing also L. A. Jones, A. W. Hull, H. E. Ives, L. 0.
Grondahl, K. T. Compton, George B. Pegram, and
Henry G. Gale.

This committee made its first formal report to the
Council of the Society at the meeting in November
1930, and I quote from its report, as follows:

“Dissatisfaction exists on the part of many physi-
cists who feel that the activity of the American Physi-
cal Society is mainly confined to quantum physics and
is not representative of physics in its broadest scope.
This feeling is quite general, and whether justified or
not, has been definitely evidenced by the formation of
such organizations as the Optical Society, the Acousti-
cal Society, the Rheology Society, and others. It is
also evidenced by the contemplated formation of a
society of Applied Physics and another society of Ap-
plied Mathematics, the latter being sponsored mainly
by mathematical physicists. The feeling is still further
evidenced by the fact that numerous papers dealing
with pure and applied physics are not even submitted
for the consideration of The Physical Review but are
published in various chemical, engineering, photo-
graphic and geological journals. This state of affairs is
a serious reflection upon the limited activity of the
Physical Society in the general field of physics.”

The Committee then went on to recommend a gen-
eral organization, somewhat similar to that of the
American Chemical Society, and that this organization
should be started by the formation of two special
divisions of the American Physical Society: one de-
voted to applied physics, and the other to mathemati-
cal physics. Each of these divisions should be, more

or less, self-governing, somewhat according to the
scheme of organization adopted by the various sec-
tions of the American Association for the Advance-
ment of Science.

It was pointed out that this proposal would be in
the nature of an experiment. The report went on to
say: “If the developments under such action are suc-
cessful, with a liberal policy of supervision and control,
it is not improbable that the organization can be ex-
tended to include the groups which have already with-
drawn from the Society.” The report further sug-
gested that such a federated organization would make
it possible to establish a central business office and
an administrative force which could serve all of the
group. It also pointed out that funds for the advance-
ment of physics would be more readily procurable be-
cause of better central and efficient business manage-
ment.

f I <HE FIRST MENTION of an Institute of Physics

A appears in the minutes of the Council of the
American Physical Society on 29 December 1930,
where several actions were taken to implement the pre-
ceding recommendations. One of these actions was to
approve the establishment of a journal of applied
physics. Another was to approve in principle the for-
mation of sections within the Society and to encour-
age the affiliation of local physics clubs. Finally, and
most importantly, the Council voted to propose the
formation of an Institute of Physics for the purpose
of coordinating various societies whose interests are
primarily in the field of physics and for the purpose of
supporting their publications.

As I recall it, the suggestion for an American Insti-
tute of Physics was first made by Dr. Foote, and the
idea immediately took hold as a constructive method
of dealing with the various complexities which I
have just described. The proposal was submitted to
the American Physical Society at its business meet-
ing on the following day, and it was there approved.

The next steps were taken at the Council meeting
of the American Physical Society in February, 1931,
at which time a Joint Committee on the Proposed
American Institute of Physics was established. This
committee consisted of Messrs. Jones, Richtmyer, and
Foote from the Optical Society of America; Fletcher,
Arnold, and Saunders from the Acoustical Society; and
Tate, Pegram, and Compton from the American Physi-
cal Society.

This joint committee promptly recommended sev-
eral steps which were approved by the organizations
concerned. These include the following:

That the American Physical Society the Optical
Society of America, and the Acoustical Society of
America cooperate in establishing the American Insti-
tute of Physics as an agency for studying the common
problems of the organizations representing physics in
America and for undertaking thereafter such functions
as the cooperating societies may assign to it.

That each of the cooperating societies designate

INSTITUTIONS OF PHYSICS

77

three members to constitute with the others so desig-
nated the Governing Board of the American Institute
of Physics.

That a full-time Executive Secretary be appointed
by the Board.

That the Institute through its Board and its Execu-
tive Secretary undertake, in such order as may be
deemed best by the Board, the study of the following
subjects with a view to making proposals to the coop-
erating societies as to functions of the Institute:

(a) Publication problems and the possibility of bene-
fits to be derived from cooperation or unification of
effort in the business of publication.

(b) Possibilities and procedures for increasing in-
come from subscriptions, advertising, and other
sources of support.

(c) Suitable publicity for meetings and contacts
with the press.

(d) Relations and contacts of the Institute with
local groups interested in physics.

That the Board investigate the possibility of de-
veloping an international management for Science Ab-
stracts A, with change of name to one more descrip-
tive, and with improvement as to indexing and com-
pleteness.

That the Board consider the development of appro-
priate relations with other national societies which
may or may not wish to become societies cooperating
with this Institute, such as the Society of Rheology,
the Meteorological Society, the Association of Physics
Teachers, and others.

At the next Council meeting on the 10th of Septem-
ber, 1931, I reported, as Chairman of this Joint Com-
mittee, that Dr. Henry A. Barton had been elected
Director of the Institute of Physics and Dr. John T.
Tate had been appointed Advisor on Publications. I
also reported the favorable action for affiliation by
other physics groups and that the Chemical Founda-
tion had given informal assurance that it was ready to
spare no expense in furthering the interests of the
Institute.

Thus was the American Institute of Physics estab-
lished, and at a Council meeting on the 28th of De-
cember, 1931, I reported to the Council that there was
no further need of this Joint Committee since its
whole purpose had been achieved in the formation of
the Institute. Dr. Darrow in his recent letter to me
states very generously in this connection that “the
committee was thereupon dissolved with honor. I
think that no other committee in the history of the
Society can have made so momentous an achievement.”

From this point on, you all know the record of this
new organization. It has served well during the past
two decades in which the profession of physics has
grown enormously both in numbers and in accom-
plishment. I think it has well solved the problem of co-
ordination of the various important fields of physics,
while at the same time giving free scope for initiative
and freedom in the development of various aspects

of the subject. It greatly alleviated the financial prob-
lem of publication, although I understand that this
problem has again caught up with us because of the
greatly increased amount of important material to be
published and the increasing costs of publication.

TN CONCLUSION, I would like, for the record, to
pay tribute to several individuals and organizations
among the very large number who have contributed to
the successful development of this enterprise.

I would pay a special tribute to our late colleague,
Dr. John T. Tate, who, as Adviser on Publications,
was principally responsible for the plan of uniform
format and centralized editorial work which promoted
economy and efficiency in publication. I would pay spe-
cial tribute to Dr. Paul D. Foote, who so effectively
guided the work of the Committee on Applied Physics,
which was so largely responsible for the solution of this
problem. The record would be notably deficient with-
out recognition of the statesmanlike contributions of
George Pegram in every stage of this program. His
knowledge of organization, law, and finance, backed up
by judgment and devoted interest, has been in-
valuable.

We owe a great deal to the Division of Natural Sci-
ences of the Rockefeller Foundation, which helped us
substantially to develop this program of scientific pub-
lication— a type of problem which was coming to the
Rockefeller Foundation from many quarters — and I
know that the Foundation took a great deal of satis-
faction in having been able to assist in the develop-
ment of this type of solution.

The Chemical Foundation helped out very substan-
tially in providing the first quarters to be occupied by
the Institute, and in underwriting a portion of the
overhead in its early operations.

Special recognition also should be given to those
physicists and friends of physics who contributed so
generously to make possible the purchase of the fine
headquarters building for the American Institute of
Physics in New York. This building has not only pro-
vided operating facilities for editorial and other acti-
vities but has been a central gathering place for physi-
cists of all categories, and it has also contributed space
for some of the work of the United Nations and other
good causes.

The Institute was especially fortunate in the selec-
tion of Dr. Henry A. Barton as its director, and we
are all greatly indebted to him and to his loyal staff
for the effective manner in which he has carried on the
executive responsibilities of this organization and for
the effective, yet very modest, way in which he has
represented the interests of American physics in vari-
ous national bodies.

I could go on to mention many others, but perhaps
it can all be summed up by saying that each and all
of those who have contributed to the development and
operation of the American Institute of Physics have
been but performing generously and effectively their
professional duty.

78

HISTORY OF PHYSICS

The first fifty years
of the AAPT

Melba Phillips

Fifty years ago there was no way for physics teachers to
communicate with each other, no way to share either their
successes or their frustrations. Teachers had no profession-
al standing as such, and teaching itself seemed to merit
little if any recognition or reward. In December 1930 the
American Association of Physics Teachers was organized as
“an informal association of those interested in the teaching
of physics.” By the end of 1931 the Association had grown
from an original 42 to more than 500. The AAPT now has
more than 10 000 members and serves the entire physics
community.

The growth of scientific societies

The first permanent scientific society of national scope in
this country was the American Association for the Advance-
ment of Science, organized in Philadelphia in 1848. In the
beginning, it had two sections: “one to embrace General
Physics, Mathematics, Chemistry, Civil Engineering, and
the Applied Sciences generally, the other to include Natural
History, Geology, Physiology and Medicine.” More special-
ized interests were later represented by the establishment
of separate sections; nine sections, including Section B,
Physics, date from 1882.

As the country grew and science developed, the needs for
communication among scientists increased. The journals
were sometimes the first response to these needs. The
American Physical Society dates from 1899, but Edward L.
Nichols and Ernest Merritt of Cornell University founded
The Physical Review six years earlier.

Melba Phillips, president of AAPT in 1 966-67, is now an emeritus pro-
fessor of physics of the University of Chicago.

PHYSICS TODAY / DECEMBER 1980

Unlike the American Chemical Society, which embraced
all aspects of chemistry, the recently-formed APS took a
very narrow view of its role. Members might raise ques-
tions of applications and of pedagogy, but the decisions of
the Council did not reflect these concerns. It is evident that
much discussion took place that did not result in actions
recorded in the formal Council minutes. A letter from
Arthur G. Webster, the person most instrumental in found-
ing the APS, to Elizabeth Laird of Mt. Holyoke College,
dated 20 November 1905, states, “I have often tried to get
the Physical Society to take up pedagogical questions, but
without success.” Applied physics and even fundamental
physics related to applications suffered much the same
neglect: the Optical Society of America came into being in
1916, partly because the Great War had cut off supplies of
optical glass from Germany, but also because most of the
influential physicists in APS took no interest in problems
involving the principles of optics. The first article in the
Journal of the Optical Society of America was written by
Floyd K. Richtmyer, who was already an influential physi-
cist; nearly twenty years later he was to write the first
article in the new journal of the American Association of
Physics Teachers.

The man who did the most to found the American
Association of Physics Teachers, Paul E. Klopsteg grew
interested in the problems of teaching physics at the
University of Minnesota, where he became an instructor in
1913 with an MA and was promoted to assistant professor in
1916 on completing his PhD.1 He did not return to
Minnesota after serving in the US Army Ordnance Depart-
ment (1917-18), but joined Leeds and Northrup Co, and
moved on to Central Scientific Co (Cenco) in 1921. He made
this last move largely because of the greater emphasis on

INSTITUTIONS OF PHYSICS

79

Three founders of the AAPT.

At left, Homer Dodge, first
president, canoeing on the White
River in Vermont in 1948. Right,
Paul E. Klopsteg in 1979, the
man most responsible for
founding the AAPT. Far right, a
1 904 photograph of Floyd K.
Richtmyer, who was instrumental
in getting AAPT welcomed into
the American Institute of
Physics. Growing up in upstate
New York, Dodge became expert
at boating at an early age.
Between 1 953 and 1 965, he
retraced John Wesley Powell’s
journey of exploration of the
Green — Colorado River Canyons,
for the most part in an open
canoe. Over the years he also
ran all of the rapids of the St.
Lawrence River, except for one
stretch that was destroyed by a
dam before he got to it.

As scientific societies proliferated in the 1 920’s and 1 930’s,

physics teachers began to realize that their specific needs could best be served

only by an association of their own.

instructional equipment at Cenco, and so remained in close
contact with physics teaching.

It became evident that many were unhappy with the lack
of attention to education in the American Physical Society.
The sales manager for Cenco, S. L. Redman, had been a
high-school science teacher himself, and was almost as
concerned with physics teaching as Klopsteg. In travelling
around the country he found William S. Webb and Marshall
N. States of the University of Kentucky to be particularly
sympathetic to the formation of a new society that would
foster teaching and communication among teachers, being
convinced that the APS would not offer the kind of forum
they needed.

In April 1928 an article by John O. Frayne of Antioch
College, entitled “The Plight of College Physics” appeared in
School Science and Mathematics.2 Frayne described the low
level of physics teaching, especially in the universities, noted
the negative attitude in APS and advocated forming a new
organization devoted to the teaching of physics. Klopsteg
got in touch with him, and they met in Chicago together with
Glen W. Warner, editor of School Science and Mathematics.
Between them they compiled a list of 115 people who might
be interested in a society of physics teachers.

The association is born

But the AAPT as it finally emerged may be said to date
from a conversation between Klopsteg, Redman and States
at an APS/AAAS meeting in Des Moines in December
1929. The result was that 30 people, chosen from the
“master list” prepared earlier, were invited to a luncheon
on 29 December 1930 during the APS/AAAS meeting. Their
avowed purpose was to launch a new organization con-
cerned with physics teaching. The man they persuaded to

chair the luncheon meeting was Homer Dodge.3 Dodge was
known to have developed a particularly successful school of
engineering physics at the University of Oklahoma.

Of the 30 invited, eight could not attend. Among those
who vigorously supported the formation of a new society
were Dodge, Klopsteg and Richtmyer. The decision was
reached in unanimous passage of a motion made by Klopsteg
“that there be organized an informal association of those
interested in the teaching of physics; that officers be elected
who shall remain in office for one year; that a committee be
established for the purpose of preparing the plans for a
formal organization; that these things be done without
prejudice toward any possible approach from other organiza-
tions or societies looking toward affiliation.” Officers were
chosen: Dodge, president; Webb, secretary treasurer and
Klopsteg, vice-president. It was also agreed that a meeting
be scheduled at the time of the forthcoming Washington
meeting of the APS, but there was more immediate work to
be done, and it was decided to meet again on 31 December,
and that those present invite others who might be interest-
ed. Forty-five people attended this second meeting, and a
preliminary constitution was adopted. Karl T. Compton
(who became a member of the first executive committee) was
present and “discussed informally the plans for the forma-
tion of the Physics Institute of America (sic) to be constituted
by an association of the several societies interested in various
fields of physics. He advised that this society [AAPT] should
take steps to cooperate with the APS in every way possible in
the formation of the Physics Institute.”

According to the minutes of the APS Council for 31
December, “The Council took notice of the organization on
this day in the Case School Physics Laboratory of a new
society to be known as the American Association of Teach-

80

HISTORY OF PHYSICS

ers of Physics (sic) . . . The Society decided to have its first
meeting in Washington at the time of the Physical Society
meeting, at which time they invited Albert W. Hull to
present an address on ‘The needs of industry in the teaching
of physics.’ The Council instructed the Secretary of the
Physical Society to make contacts with the new Society and
to give them proper place on the first day of the Physical
Society’s Washington program.” The address by Hull, who
was director of research at General Electric Company, was
actually entitled “Qualifications of a Research Physicist,”
and was later printed in Science ,4 It drew a large audi-
ence— other sessions were practically deserted — and Comp-
ton led a lively discussion.

Gaining the recognition of the AIP

Meanwhile the organization of the American Institute of
Physics was proceeding. The first formal meeting was held
1 May 1931. Four societies participated: the Optical
Society of America, the American Physical Society, the
Acoustical Society of America, and the Society of Rheology,
the last two having been organized in 1929. The AAPT was
not invited; grave doubts by some as to the “eventual
stability and success of AAPT” are reflected and refuted in a
letter from Klopsteg to Compton, who was the first chair-
man of the AIP governing board. As a result of letters from
both Klopsteg and Dodge and some intervention from
Richtmyer, as well as a very successful first annual meeting
of AAPT in December 1931 and the adoption of a more
formal constitution, the AIP board, in February 1932,
“expressed themselves unanimously as desiring your associ-
ation to be included with the other founder societies of the
AIP,” and asked that three representatives be appointed to
the board. Those chosen were Dodge, Klopsteg and Fre-
deric Palmer of Haverford College. Klopsteg remained on
the board until 1951 with a hiatus of only two years, and he
was chairman of the board during 1940-47.

The AIP arose largely from the fragmentation of societies
of physicists. According to Compton, “In one sense the
American Institute of Physics is the child of the five parent
national societies which have cooperated in forming it. In
another sense, however, it has followed the more usual
course of being born of two parents, the one financial
distress and the other organizational disintegration.”5 Fi-
nancial help was secured from the Chemical Foundation, a
corporation formed by major chemical companies to take
over German-owned patents after World War I. Its net free
earnings were to be “used and devoted to the development
and advancement of chemistry and allied sciences . . .” The
impetus for the formation of AIP actually came from the
Chemical Foundation, whose support was contingent on a
“unified association of American physicists.”

By late December 1931 a great deal of progress could be
reported at the first annual meeting of the American
Association of Physics Teachers, which was held in New
Orleans with APS and AAAS. Of special significance was
the appointment of a committee, headed by Webb, to
develop ways and means of publishing a journal. The first
issue of the American Physics Teacher (later to become the
American Journal of Physics) appeared in February 1933
under the editorship of Duane Roller, then at the University
of Oklahoma. Its lead article was entitled “Physics is
Physics;”6 in it Richtmyer pointed out that there are several
aspects of physics— research and teaching, either at the
high-school or college level — but they are still physics. But
in his opinion “Teaching is an art and not a science.”
Although then only a quarterly the journal taxed the
slender resources available; it was recommended that dues
be raised from the original $2.00 to $3.00, and the change
was later approved by a membership ballot.

Palmer had been something of a pioneer in the teaching of
physics. His article, “Some properties of atoms and elec-
trons as measured by students,”7 a justification for and

description of an advanced undergraduate laboratory, had
caught Klopsteg’s attention and Palmer was invited to
participate in the founding of AAPT. One particularly
significant step taken in 1933 was to start the ball rolling to
prepare an “encyclopedia” of lecture demonstrations; the
idea was suggested by Claude J. Lapp of the University of
Iowa. Palmer was instrumental in seeing that it was
carried through: “I just went ahead and paid the bills to the
extent of somewhere around $1500,” he recalled. He also
made available personnel and facilities at Haverford Col-
lege; Richard M. Sutton of Haverford was the capable editor
of Demonstration Experiments in Physics, published in 1938.
The book was an immediate success; according to Palmer,
“the 15% royalties amounted to enough so that I was paid
back . . . within three years. It’s one of the best investments
I ever made, I think.”

At the December 1934 meeting in Pittsburgh an anony-
mous donor offered to finance for a period of three years an
annual award (a medal and a certificate) for notable
contributions to the teaching of physics. This form of
recognition was to become the Oersted Medal, and the donor
was later revealed to be Klopsteg. The first award, an-
nounced at the annual meeting in December 1936, was
given posthumously to William S. Franklin (1863-1930).
Franklin was described as a man of exuberant energy “who
boasted that the teaching of physics was the greatest fun in
the world.” He was known for his frequent keen and
clarifying comments on papers presented at Physical Soci-
ety meetings, and he wrote prolifically — twenty-five vol-
umes of textbooks, many contributions on “Recent Ad-
vances in Physics” in School Science and Mathematics, and
a popular volume of educational essays dealing with the
beauties of nature, in addition to his research papers.
Much of his career had been spent at Lehigh University and
MIT, and the Association placed bronze memorial tablets in
the physics laboratories of both those institutions. If his
death had not come in June 1930, the result of an auto-
mobile accident, he would have surely taken a prominent
role in the organization of AAPT.

INSTITUTIONS OF PHYSICS

81

◄

A 1928 summer institute of the Society for
the Promotion of Engineering Education (now
the American Society for Engineering Educa-
tion) at MIT. Here Paul Klopsteg spoke infor-
mally with people who taught physics to engi-
neers. Posed in the front row are, from left to
right: William S. Franklin, who was awarded,
posthumously, the first Oersted Medal; A.
Wilmer Duff, director of the institute and au-
thor of the physics text most widely used for
many years, and O. M. Stewart. Behind Duff
is Henry Crew and behind Stewart is Klop-
steg. Klopsteg recalls a great unanimity of
sentiment at that meeting in favor of an
organization like AAPT.

Richtmyer’s contribution to the first issue of
the American Physics Teacher (later to be-
come the American Journal of Physics), in
which he argues that a successful physics
teacher must have more than a thorough
knowledge of physics — he must acquire the
"art of teaching.” ^

The AMERICAN

PHYSICS TEACHER

Volume 1 FEBRUARY, 1933 Number 1

Physics is Physics'

F.K. Richtmyer, Department of Physics, Cornell University

PERHAPS I can best elucidate the rather cryptic
title of this paper by quoting a remark of the late
Professor G.W. Jones, Professor of Mathematics at Cornell
University from 1877 to 1907 and one of the best teachers
who ever occupied a professorial chair. It is told that an
embryo teacher, taking one of Professor Jones’courses, once
asked him: “What must one do to become a successful
teacher of mathematics?”; to which Jones replied: “To
become a successful teacher of mathematics one must
acquire a thorough knowledge of mathematics.”

I am sure that every member of Section Q, and
probably many educationists, would agree with Professor
Jones’ statement, as far as it goes. I am equally sure that
these same persons would agree at once with the converse
statement that no person can become a successful teacher
of any subject unless he possesses an adequate knowledge
of that subject, even though that person may have had all
of the courses in education given in one of the larger
universities — 79 of them at Cornell! May I point out,
however, parenthetically, that the impression seems to be
rather prevalent that there is another group of persons,
composed r ’ 'cationists and

educatio with this

secc

from the fact that there are many excellent scholars who
are poor teachers. (I hasten to add, hovyever, that many
such scholars who are seeming failures as teachers of the
more elementary branches of a subject are most inspiring
teachers of the more advanced courses.) Something else
than a knowledge of the subject is necessary. That
something is, I believe, the acquisition of the art of
teaching. And it is primarily to this last statement that I
wish to direct my remarks.

Teaching, I say, is an art, and not a science. In a recent
address before Science Service2 Dr. Robert A. Millikan
characterized a science as comprising first of all “a body of
factual knowledge accepted as correct by all workers in the
field.” Surrounding this body of knowledge is a fringe,
narrow or wide as the case may be, which represents the
controversial part of the science. And outside of this fringe
is the great unknown. Investigators are constantly exploring
this controversial region; making hypotheses and theories;
devising experiments to test those theories; and gradually
enlarging the boundaries of accepted facts. Without a
reasonable foundation of accepted fact, no subject can lay
claim to the appellation “science.”

If of a science be accer»,f' ’ J

The Oersted presentation was not at first part of any joint
ceremonial session as was the Richtmyer Memorial Lecture,
but that has changed. For many years now, both events
have been part of the ceremonial session, and both are
regarded as prestigious honors.

Meetings, members, honors and awards

The pattern of AAPT meetings evolved gradually. After
the AAPT was organized at an APS/AAAS meeting, AAPT
meetings were held at those joint meetings until 1939, and
at the APS meetings after that. In 1943 the annual
meeting was shifted to January, and has remained so with
only a few exceptions. The summer meetings were also
joint at the beginning, but have been strictly AAPT affairs
since the mide-1950’s. These meetings are hosted by
colleges or universities, and are on the whole less formal
than the winter meetings.

At first, members of the AAPT were elected by the
executive committee with a two-thirds majority needed for
election. Those eligible were “(a) teachers in institutions of
collegiate grade; and (b) those whose interest in education is
primarily in physics of college and university grade.” In
December 1933 election of members was delegated to the
officers, and there was much discussion in the executive
committee of what was called “the secondary-school prob-
lem.” The consensus of opinion was that requirements for
admission be changed so that it would be possible for more
secondary-school teachers to become AAPT members, but
the constitution seemed to read otherwise. The solution
arrived at was a new interpretation of eligibility require-
ment (b) above: “the executive board rules that all teachers
of physics who have professional qualifications equivalent
to those required of teachers of college physics are eligible
for membership in the association.” The quite unwarrant-
ed fear that the association might be taken over by the
athletic coaches who taught physics in many of the small
high schools of the day persisted for a number of years. Only
in 1938 was eligibility requirement (b) changed to read
“other persons whose election will, in the judgement of the

Council, promote the objectives of the Association.” Also in
1938 the category of junior membership was established to
admit college and university students with a major interest
in physics and two years of college physics or the equiv-
alent. The name of this category was changed from
“junior” to “student” in 1975.

Despite the differences of opinion on the eligibility of
many high-school teachers for membership, the AAPT paid
a great deal of attention to the high-school teaching of
physics from the beginning. As early as 1934, “support for
work on the improvement of teaching in secondary schools”
was listed as one of the major tasks of the Association.
Prominent leaders in this area were Karl Lark-Horowitz of
Purdue University and Robert J. Havighurst, the x-ray
crystallographer well known for analysis of the structure of
rock salt before he turned to social science and science
education. Much of the emphasis was put on the problems
of preparatory and continuing education for teachers.
Teacher certification requirements in the various states
merited much attention, particularly during the years that
most students attended small schools, in which “one and the
same teacher has to divide his attention among a great
many unrelated tasks.” Awards for high schools and for
high-school teachers were set up later on; the exact nature
of these awards for excellence in physics instruction has
varied from time to time, but such programs have been
continued and strengthened.

The Distinguished Service Citations “for important con-
tributions to the teaching of physics” were initiated in
1952. The number of these awards per year has varied from
two to ten; they are usually given to teachers but occasional-
ly to other types of contributions to physics education.

It should be noted that none of the AAPT honors is
restricted to members of the Association. The most recent-
ly established honor is the Millikan Lecture Award. It is
used not only “in recognition of an individual for notable
contributions to the teaching of physics” but also to serve as
a highlight of the summer meeting. The first lecturer
chosen by the committee (in 1964) was H. Victor Neher of

82

HISTORY OF PHYSICS

Caltech, a student and colleague of Millikan, but the
lectureship had been made retroactive so that a lecture by
Klopsteg in 1962 was designated as the first lecture. A
medal accompanies this award.

Although not precisely an award it has been an honor
since 1940 to be chosen to give the Richtmyer Memorial
Lecture. Richtymer died unexpectedly in November 1939,
and a proposal for the lectureship was approved the
following year. The first Richtmyer Lecture was delivered
by Arthur H. Compton on 30 December 1941. This was less
than a month after Pearl Harbor, and Compton’s title was
very appropriately “War Problems of the Physics Teach-
er.” This address has been reprinted in the volume On
Physics Teaching (1979). The official description of the
lectureship appears in a statement of policy approved by the
AAPT Council on 30 January 1956: “It is not expected that
the lecture should reflect any particular interest of Profes-
sor Richtmyer; the topics chosen for it are, rather, those in
which he would have found interest were he still alive.”

The war years and after

The Association was deeply involved in World War II,
particularly in education and manpower. Many of its
members, including several officers, went on leave from
their teaching posts to work full time for the government
directly or in war research laboratories, and other war-
related activities were undertaken by the Association it-
self. Special committees prepared reports, and served to
advise on training in physics both inside and outside the
armed forces. The AAPT also worked with the War
Policies Committee, which was established by the American
Institute of Physics and chaired by Klopsteg. As the war
progressed it became increasingly difficult to obtain equip-
ment for teaching physics, and the Association, through the
War Policies Committee, pressed for higher priorities for
essential scientific teaching equipment.

It was clear almost from the start of the war that physics
and physics teaching could never be the same again, that
both would have new responsibilities in the world to come.
Early in 1942 Edward U. Condon was already writing of “A
Physicist’s Peace.”8 Condon’s concern for the social impact
of physics was as great as his interest and enthusiasm for
every facet of the subject itself.

The Oersted Response of George W. Stewart in January
1943, entitled “Teaching of Tomorrow,” anticipated
postwar changes, and stressed the necessity of making
physics teaching even more useful to society. Vern O.
Knudsen, who had been one of the founders of the Acousti-
cal Society, charged in “The Physicist in the New World”9
that we have trained too few students “to take important
responsibilities in the practical world, and certainly too few
to be independent scholars, thoroughly trained in funda-
mental and applied physics.” The emphasis was dual: the
education of professional scientists must be broadened, and
science education must include the study of the relations of
science to other human activities. Side by side with the
strengthening of the curriculum within the discipline of
physics there was an upsurge of interest in the role of
physics in general education.

Interest in physics education increased markedly during
the 1950’s and so did the activities of the AAPT. The
Apparatus Committee must be singled out for special
attention, working on its own and also with the American
Institute of Physics. An intensive study of apparatus used
in physics teaching was carried out, and several valuable
publications were prepared. In January 1959 the first
Competition for New and Improved Apparatus was held at
the annual meeting; this competition has been a popular
feature of alternate meetings since that time. A new book
on demonstration apparatus got under way. AAPT and
AIP undertook a visiting scientist program for both colleges
and high schools.

J. W. Buchta, first executive secretary ot the AAPT and first editor of
The Physics Teacher, as sketched by Fern Barber in the late 1950’s.

The Association was much involved in the early efforts to
support institutes for the continuing education of teachers,
with J. W. Buchta of the University of Minnesota among the
prime movers. The American Journal of Physics was able
to expand; Thomas H. Osgood of Michigan State had taken
over the editorship from Roller in 1948, and was succeeded
by Walter C. Michels of Bryn Mawr ten years later, during a
period of continuous growth. Michels, with his Falstaffian
figure and red beard, was an influential figure in physics for
i^any years. During his tenure as editor he often regretted
the necessity for page charges, and would be delighted that
the Association has now been able to dispense with them.

The second AAPT journal, The Physics Teacher, dates
from the early 1960’s. The national concern for high-school
science teaching had grown during the late 1950’s. The
Physical Science Study Committee, initiated in 1956 under
the leadership of Jerrold R. Zacharias and Francis L.
Friedman of MIT, had produced PSSC Physics, and the
National Science Foundation was supporting both Summer
Institutes and Academic Year Institutes for the continuing
education of science and mathematics teachers. It was
clear that the AAPT should be of service to all physics
teachers, including those in high schools, but broadening
the American Journal of Physics to emphasize high-school
concerns did not seem feasible. Under the leadership of
Malcolm Correll, then AAPT president, a prospectus for a
new journal was prepared in 1961, and a proposal was made
to NSF for a grant to help it get under way. The first editor
was Buchta, who was also the first executive secretary of the
Association. He had served as editor of both the Physical
Review and Reviews of Modern Physics, and had much first-
hand acquaintance with American high schools. According
to the masthead, “The Physics Teacher is dedicated to the
enhancement of physics as a basic science in the secondary
schools.” Through the NSF grant all teachers of high-
school physics received the journal without charge for the

INSTITUTIONS OF PHYSICS

83

Six former presidents of AAPT, caught here seated together in the
second row at an AAPT meeting held earlier this year at Rensselaer
Polytechnic Institute. They are, from left to right, Melba Phillips

first year. The first issue was that of April 1963. In 1968 it
came into the capable hands of Clifford Swartz, SUNY,
Stony Brook. Under the new editor and his associate
editors (first Lester G. Paldy and then Thomas D. Minor)
high-school physics is still central, but the journal embraces
the teaching of introductory physics at all levels. It
contains much of practical value, but its approach is by no
means narrowly utilitarian. The Physics Teacher may be
selected as the membership journal by AAPT members, or
taken at a reduced rate in addition to the American Journal
of Physics. (For a detailed history of the early years and an
appreciation of Buchta, see the tenth anniversary issue of
The Physics Teacher , April 1973.)

Establishment of an executive office

Until 1957 the Association had operated as an unincor-
porated body, but corporation papers were drawn up that
year; the immediate reasons were to put the organization in
a stronger legal position to deal with employees and to
accept possible bequests. Not that there were many em-
ployees: the AAPT from the beginning was the product of
volunteer labor except for secretarial help needed for the
journal and to facilitate committee work as necessary. Even
for that there was a great deal of institutional help, as there
is now, from colleges and universities at which officers were
resident, and in the early days Klopsteg made use of Cenco
secretarial personnel. But the work of the AAPT expand-
ed, with some funding assistance from NSF and other
agencies, and the level of activities rose in the decade of the
1950’s. In 1962 the Association was able to establish an
Executive Office for the first time. Buchta was the first
executive secretary; on retiring from the University of
Minnesota he set up shop in Washington, initially with
space rented from the National Science Teachers Associ-
ation. A glutton for work, Buchta launched the new
journal, The Physics Teacher , handled the collection of

(president 1966-67), Robert N. Little (1970-71), James B. Gerhart
(1978-79), Janet B. Guernsey (1975-76), Stanley S. Ballard (1968-
69), and Robert Karplus (1977-78). Photograph by Reuben Alley.

AAPT dues and did what seems a thousand other things in
addition to taking care of the Association business. It was
nearly a one-man operation, except for typing and filing.

Buchta had always been a man of boundless enthusiasm
and vitality; amid the inevitable respiratory infections of a
Minnesota winter, which not even he could escape entirely,
his undiminished cheerfulness and enterprise was almost
exasperating. But after a brief illness his death came in
October 1966, a blow to the Association since no backup had
been provided. AAPT veterans and novices alike rallied to
the aid of the officers in meeting the emergency. I was
president at the time, and recall with pleasure the coopera-
tion of many people in meeting the demands of the Execu-
tive Office. Since that time editing The Physics Teacher has
been a separate operation, and dues collection, along with
the maintenance of mailing lists, has been handled by the
American Institute of Physics. The Association was very
fortunate, at this critical time, in securing the services of
Mark Zemansky as executive secretary. Zemansky, a
former president of AAPT and retired from teaching, lived
near New York, and it was possible to arrange for office
space at the American Institute of Physics.

By 1968 it was evident that NSF would phase out the
several national education commissions in scientific disci-
plines. The AAPT had from the start been very intimately
involved with the Commission on College Physics, and it
seemed to be the Association’s responsibility to take over
many of the activities and duties of that Commission.

The Commission on College Physics

To understand the existence and the role of the Commis-
sion on College Physics it is necessary to recall that the
1950’s saw great intensification of interest in science
education, particularly in physics. Physicists had contrib-
uted enormously to the winning of World War II, and people
trained in physics had expanded their range of skills. New

84

HISTORY OF PHYSICS

opportunities for employment arose in industry and in
academic life; physicists had learned to extend their exper-
tise to borderline and interdisciplinary fields as well as to
many applications outside the demands of pure research.

Immediately after the war so many young people with
experience in war laboratories or with sophisticated equip-
ment in the field returned to study physics professionally
that even the expanded market seemed to be satiated in the
early 1950’s, but things changed. It must be admitted that
the Cold War played a not insignificant part in the renewed
demand for physicists. The development of sophisticated
weapons had not ended with the defeat of Hilter and
Mussolini; this effort was if anything enhanced in the
1950’s. The physicists active in education were not them-
selves motivated by the Cold War, but so many humanitar-
ian reasons for improving education can always be found
that they were glad to take advantage of the funds available
for this purpose.

It is sometimes said that the Soviet launching of Sputnik
in October 1957 led to all these efforts; that is not true, but
there is no doubt the efforts were spurred by this event, and
more Federal financing became available. That the USSR
could surpass American technology in this fashion was an
unexpected blow to American pride and causes were
sought. President Eisenhower commented over a nation-
wide TV network: “According to my scientific friends, one
of our greatest and most glaring inefficiencies is in the
failure of us in this country to give high priority to scientific
education.”10 Federal support of science education was
forthcoming, and physics received the greatest amount, at
least at first, partly because physics is basic to the technol-
ogy required to build and launch missiles.

Until the very late 1950’s NSF largely confined its
support of science education to pre-college, predominantly
high-school, study. The extension to college physics was
promoted both within and outside the AAPT, particularly
by the MIT contingent spearheaded by Zacharias, already
engaged in the Physical Science Study Committee. The
establishment of a separate commission was explicitly
recommended in the report of three conferences held during
1959-60. The rationale was put cogently by the steering
committee: “The development of physics teaching in the
United States colleges and universities has largely been the
result of individual efforts . . . The increasing role of physics
in our scientific progress, in our technology, and in our
society and culture, as well as the rapid advances taking
place within physics itself, demands consideration of new
approaches to the improvement of physics teaching. These
should be broadly coordinated and national in scope.”11 The
conference report described the basic aims of college physics
courses and suggested activities to achieve them. There was
a strong recommendation for the establishment of a “Com-
mission for the Improvement of Instruction in College
Physics.”

A grant from NSF brought the Commission on College
Physics into existence later in 1960. The Commission met
four times a year, arranged and ran a large number of
conferences, issued many publications and encouraged the
development of a multitude of teaching aids.

By 1968 it had become evident that a surplus of profes-
sional physicists and physics teachers was in the making,
and federal support of physics education began to dimin-
ish. In January 1969 the Commission was explicitly re-
quested to plan an orderly phaseout, which was finally
completed in August 1971. Many of the Commission’s
activities, duties and responsibilities had either to be taken
over entirely by AAPT or abandoned. Zemansky wished to
be relieved of his position as executive secretary in 1970,
and it was at this time that the Executive Office was
revamped to take on the larger role envisioned for AAPT.

Wilbur V. Johnson, on leave from Central Washington
State College, became Executive Officer in 1970, and opened

an office in Washington D.C. He was succeeded by Arnold A.
Strassenburg in September 1972, and the office was moved
to Stony Brook, where it has remained. The Association’s
efforts to continue and to expand the Commission’s services,
coupled with retrenchment on the part of governmental and
other sources of funds and the onset of double-digit inflation
threatened the stability of the organization in 1973. The
journals were particularly vulnerable to inflation: the
price of paper rose by 30% in less than two years, and
publication costs to the Association increased by 32% in the
same period. Fortunately the leadership, notably the
president, E. Leonard Jossem, was able to handle the
situation. Rather stern measures were called for, and the
person who put them into effect was Strassenburg, who
managed to continue the expansion of services at the same
time. There are Association members who still wince at
what they consider his penny-pinching, however much they
appreciate his capable and untiring efforts on behalf of the
organization. Except for the two regular journals, most of
the work of AAPT is carried out by or through the Executive
Office.

Some of the activities begun during the life of the
Commission were joint with AAPT from the beginning or
were assumed entirely by AAPT almost from the start. The
preparation of Resource Letters, annotated bibliographies
on specific topics, had been introduced by Gerald Holton,
then a Commission member. The Resource Letters appear
first in the American Journal of Physics, and many of them
were supplemented by Reprint Booklets containing some of
the most useful papers cited in the parent letter.

Another ongoing activity fostered by the Commission is
the Film Repository. This service was subsidized by the
Commission during its first year, 1969, then taken over
entirely by AAPT. Satisfactory film notes are mandatory,
as is sound physics and technical excellence. The pricing is
such as to cover only the cost of production; no remunera-
tion goes to the maker of the film. The Film Competition
has been a feature of the annual meetings in even-num-
bered years since 1968, alternating with the Apparatus
Competition. Winning films in the competition are eligible
for the Repository, provided they are accompanied by
adequate explanatory notes for instructional use. Another
part of the Film Repository is the distribution of sets of 35-
mm slides that have been produced and developed by
physics teachers. Each set of slides is accompanied by a
Teacher’s Guide.

Increasingly the Executive Office also makes available
documents of other types. These can be categorized as
follows:

► compilations of information useful to physics teachers,
for example an annotated bibliography of films;

► reprint books of articles on specific topics from the AAPT
journals, for example, Apparatus for Physics Teaching-,

► instructional materials for students, such as a module on
the bicycle; and

► conference reports, topical listings and journal reprints from
a resource known as Information Pool, which was originally
maintained by the American Institute of Physics. Typically
the need for these products is identified by an AAPT member
on committee. The production, marketing and order fulfill-
ment are managed by the Executive Office.

Among the duties of the executive officer is the publication
of the AAPT Announcer. The Announcer was started by John-
son in 1971, and is published four times a year and is sent free
to all AAPT members; the May and December issues carry ad-
vance programs for the national meetings. The Announcer has
grown steadily in coverage and importance.

The growth of local chapters

Local chapters of AAPT were authorized as early as April
1931, and the first chapter was recognized in 1932. The

r

INSTITUTIONS OF PHYSICS

rationale for their existence has been primarily to provide
meetings accessible to AAPT members and others interest-
ed in physics teaching. Individuals may be members of
chapters (sections since 1947) without being AAPT mem-
bers, and many AAPT members are not associated with any
section. There are now 37 sections. The newest and one of
the largest and most active is the Ontario section; most of
the others have boundaries corresponding to states. All
sections are represented on the Council of the Association,
and the chairman of the section representatives is an
influential member of the Executive Board. Sections form
a vital and important part of the organization, but they do
not help to meet one recurring difficulty: they make no
direct contribution to the national treasury.

According to Dodge, who as first president was in a
position to know, “finances were a serious problem right
from the first minute. One reason was that physics
teachers, then and now (1963), don’t have much money.” I
have noted that Klopsteg financed the Oersted Medal in the
beginning, and that Palmer advanced the costs of preparing
the book on demonstrations; we find that somewhat later
Marshall States contributed $500 to help initiate a volume
of advanced undergraduate experiments as a memorial to
Lloyd W. Taylor. To keep the Journal afloat, Richtmyer in
1937 obtained a grant from the Carnegie Corporation:
$7500 to be spent over a five-year period.

The Association survived and remained active, but its
funds were modest. Sears sometimes recalled in later years
that when he became treasurer in 1952 the budget was
prepared at a portable blackboard during annual executive-
committee meetings. Records show that the first budget he
proposed was $18 600. Now the gross budget amounts to
more than three quarters of a million dollars and is the
result of much advance preparation. It is true that the
consumer price index has risen by a factor of four since
1952, but services to members and other physics teachers

85

have multiplied by an order of magnitude. Most of these
new services have been introduced within the past ten
years, with the expansion of the Executive Office and wider
committee activity.

There has been corresponding growth in meeting partici-
pation. Not only do meetings provide interesting papers
and a forum for members but also tutorials on special topics
and a multitude of workshops on many activities — most
recently microcomputers, computers and programmable
calculators, along with holography, have been especially
popular.

It is impossible to put a period to a sketch of only fifty
years of activity in behalf of physics teaching. There has
never been a time when the variety and intensity of effort
on the part of the Association has been greater. The AAPT
is celebrating its anniversary by looking to the future — a
time that will undoubtedly be more challenging than any
before.

References

1. M. Phillips, Phys. Teach. 15, 212 (1977).

2. J. Frayne, Sch. Sci. Math. 28, 345 (1928).

3. J. Guernsey, Phys. Teach. 17, 84 (1979).

4. A. Hull, Science 73, 623 (1931).

5. K. Compton, Rev. Sci. Instrum. 4, 57 (1933).

6. F. Richtmyer, Am. Phys. Teach. 1, 1 (1933) (reprinted in Phys
Teach. 14, 30 (1976)).

7. F. Palmer, J. Opt. Soc. Am. 7, 873 (1923).

8. E. Condon, Am. J. Phys. 10, 96 (1942).

9. V. Knudsen, Am. J. Phys. 11, 78 (1943).

10. “Eisenhower Speaks on Science and Security,” Bull. At. Sci 13
359 (1957).

11. “Report of Conference on the Improvement of College Physics

Courses,” Am. J. Phys. 28, 568 (1960). □

86

HISTORY OF PHYSICS

The giant cancer tube and the
Kellogg Radiation Laboratory

The early history of the world-famous nuclear physics laboratory
involves a Nobel Prize winning physicist, a wealthy physician, the
developer of a million-volt x-ray tube, and the cornflake king.

Charles H. Holbrow

Fifty years ago the W. K. Kellogg Labo-
ratory of the California Institute of
Technology was founded as a center of
radiation therapy. Seven years later it
abandoned medicine to pursue its de-
velopment into what is today an inter-
nationally known center of nuclear
physics. The behind-the-scenes negoti-
ations surrounding the laboratory’s
founding, early history and abrupt
change in direction give unusual in-
sight into the administrative style of
Robert A. Millikan, Caltech’s chief ex-
ecutive. The early history of the labo-
ratory was shaped in important ways
by this Nobel Prize winning physicist’s
successes and failures in raising sup-
port money. His efforts, including a
13-year long attempt to take a horse
farm away from the University of Cali-
fornia, reveal why Millikan was so
successful as head of Caltech, and show
that it was just as difficult then to get
support for pure research in a new field
of physics as it is today.

The laboratory, established in 1931
to do research in the x-ray treatment of
cancer, included a subordinate pro-
gram of research in physics. What led

Charles H. Holbrow is Professor of Physics at
Colgate University. In the summer of 1980 he
was Visiting Associate at the Kellogg Radiation
Laboratory of the California Institute of Tech-
nology, where this article was prepared.

to the events of 1938, when the physics
program entirely supplanted the medi-
cine? The direction of the laboratory,
from the time of its founding through the
time of this change and beyond, is tied to
the interests and personalities of four
men.

► Robert Millikan was so prominent
and so completely identified with Cal-
tech as a whole that we might overlook
his special role in establishing Kel-
logg. His success as a fund raiser
launched the lab; his vision fostered it;
his influence protected its fragile pro-
gram of pure research; and, finally, one
of his rare failures as a fund raiser
freed it from cancer research.

► Seeley G. Mudd, the physician son of
a wealthy mine owner, played a role
largely unknown until now. Yet he
was a prime mover in creating the lab,
in determining its purpose, and even in
administering it. Only after he ended
his participation did the lab change
sharply in purpose and function.

► Charles C. Lauritsen, a Danish engi-
neer, provided the innovation that was
reason to create the lab — the million-
volt x-ray tube. Also, it was Lauritsen
who led the lab through that golden
decade of nuclear physics before World
War II, when Kellogg established its
international reputation as a center of
nuclear research.

► W. K. Kellogg of Battle Creek,
Michigan, the eponym himself, pro-
vided the funds to build the Kellogg

PHYSICS TODAY / JULY 1981

Radiation Laboratory in 1931. Al-
though he never fully understood what
his money supported, especially as the
work shifted more and more to nuclear
physics, Kellogg believed in Millikan
and contributed the operating expenses
of the lab in certain critical years. He
also drew Millikan into a bizarre fund-
raising scheme to have the University
of California shift millions of dollars of
its endowment to Caltech for the Kel-
logg Radiation Laboratory.

Millikan and Lauritsen

In 1931, Caltech was quite a young
institution. In 1891 Amos G. Throop,
then 80 years old, founded Throop Uni-
versity, which two years later became
Throop Polytechnic Institute. By 1901
the Institute consisted of over three
hundred students distributed among a
college, a normal school, an academy
and a grammar school. In 1907, how-
ever, the Trustees decided to start over
and create a first-class technical insti-
tution. They split off the elementary
school, hired a new president, and a few
years later changed the name to
Throop College of Technology.

In 1911, the year the college moved to
its present location in Pasedena, 31
students were enrolled. By 1921, the
year after the name was changed to
California Institute of Technology, en-
rollment had grown to almost four
hundred, but only 15 were graduate
students. The next decade, however,

INSTITUTIONS OF PHYSICS

87

'

saw Caltech move toward eminence in
research as the number of buildings
increased from three to eight and grad-
uate enrollment grew more than
twelvefold. By 1931 the Institute was
11 years old — or 24 years old or 40
years old, but young and vigorous any
way you counted its age.

Millikan’s arrival in 1921 had much
to do with the new Institute’s rapid
growth. Millikan was lured to Caltech
from the University of Chicago by an
exceptionally loyal, dedicated and gen-
erous group of Trustees who promised
strong support for research in physics.
Arthur Fleming, Chairman of the
Trustees, promised $90 000 a year just
for physics research. Also, if Millikan
would come, Fleming agreed to pledge
his fortune of $4.2 million to Caltech.

Although never officially “Presi-
dent,” Millikan was the chief executive
officer and was recognized as such. His
extensive acquaintances, his personal
charm, and his remarkable intuition as
to what and who were important in
physics enabled him to draw to Pasade-
na outstanding faculty and visitors:
Tolman, Epstein, Lorentz, Einstein,
Oppenheimer, to name a few. Nation-
al Research Council Fellows came to
Caltech in substantial numbers, and
directly or indirectly Millikan also at-
tracted good graduate students.

In 1926, Charles Lauritsen, a Danish
engineer working for a manufacturer
of radio sets, attended a lecture in St.
Louis by Millikan. Inspired by Milli-
kan, Lauritsen moved his family to
Pasadena and at age 34 began work for
a PhD. His thesis, completed in 1929,
was a study of electron emission from
metals in intense electric fields.

Work with high voltages and with
field-emission electrons naturally in-
volved Lauritsen with x rays. At that
time no one had been able to design a
single-stage x-ray tube that would ex-
ceed 350 kV. The principal problem
was flashover due to the production of
regions of high charge on insulators in
the tube by backstreaming electrons.
Lauritsen produced and patented a de-
sign with metal shields to protect the
tube from backstreaming, and with a
primitive ancestor of the equipotential
rings of a Van de Graaff tube to smooth
out the potential gradient. His tube
could hold over one million volts.

There were obvious medical uses of
such a tube. He wrote in his patent
application of 1930
I have found that when [1000 000
volt] potentials are employed, radi-
ations substantially the frequency of
the gamma radiation from radium
may be obtained from the tube em-
bodying my invention.

Such tubes can therefore be em-
ployed as the full equivalent of ra-
dium in the treatment of disease, or
for therapeutic purposes.

Robert Andrew Millikan and Charles C. Lauritsen (left) stand atop a million-volt x-ray tube in
the High Tension Laboratory at Caltech around 1930 or 1931. (Photograph courtesy of the
Archives, California Institute of Technology). Figure 1

88

HISTORY OF PHYSICS

cine at Harvard and received his MD in
1924. After three years of internship
and residency at Massachusetts Gener-
al Hospital, he returned home to Pasa-
dena, a physician with experience in
radiology as well as useful contacts in
the medical profession.

In view of the close relation of the
Mudd family to Caltech, it was as
natural for Millikan to turn to Mudd as
it was for Mudd to be interested in
possible therapeutic uses of the
1 000 000 volt x-ray tube. Millikan
enlisted Mudd’s help in several ways.
They decided to undertake a five-year
study of the effectiveness of 750 kV x
radiation in the treatment of cancer
compared to the effectiveness of the 200
kV radiation then available from com-
mercial tubes in hospitals. The plan
called for expenditure of about $20 000
a year, roughly half of which would
permit Mudd to sponsor and evaluate
the treatment of several hundred pa-
tients over several years; the other half
would fund a supportive program of
physical research in which Lauritsen
would continue his studies of high-
voltage phenomena.

Again the Mudd family acted. Della
Mudd, Seeley G. Mudd’s mother, anon-
ymously donated $75 000 for the pro-
ject. (The 1931 dollar was worth six to
seven times the 1981 dollar.) Seeley G.
Mudd himself agreed to serve without
salary as resident radiologist in the
treatment center. As it turned out, in
several years he also paid a large part
of the operating costs of the project.

Mudd did the leg work of assembling a
panel of local doctors to oversee the ad-
ministration of the project, although Mil-
likan wrote the coaxing letters to them.
Millikan also saw to the publicity, which
was vigorous. Figure 2 is a photograph
that was described as showing the,
“World’s Largest X-ray tube.” Through-
out 1931 and 1932 the headlines of the
Pasadena Star-News, the Los Angeles
Times, and the Los Angeles Examiner
shout the same rhetoric as our own re-
cent “war on cancer.” Millikan was never
shy about his accomplishments or those
of Caltech, and he was very successful in
raising money, facts which inspired the
famous graffito shown in figure 3.

Kellogg and the laboratory

By late 1930 plans for construction of
a building to specialize in cancer ther-
apy were being drawn. Early in 1931
the estimates came in at $94 000, a sum
uncomfortably greater than the
amount promised by Mrs. Mudd.

Suddenly the fourth founder appears
on the scene. In March 1931 the first
correspondence between Millikan and
W. K. Kellogg appears. The 71-year
old Kellogg (figure 4) had come from
Battle Creek, Michigan, to winter at his
Arabian Horse Ranch in Pomona, Cali-
fornia, where since 1925 he had bred

In fact, even before the patent was
filed, Millikan and Lauritsen had be-
gun to launch a program of research on
the treatment of cancer with x-rays.
Figure 1 shows Millikan and Lauritsen
standing on the tube in the High Ten-
sion Laboratory where it was built and
where the first patients were treated.
From this work grew the Kellogg Radi-
ation Laboratory.

Seeley G. Mudd

In 1930 Caltech began to suffer from
the Great Depression settling on the
United States. Within a year Fleming
had lost his $4 million fortune pledged
to Caltech. Trustees and donors more
fortunate than Fleming rallied to help
the Institute pay its debts. For exam-
ple, Della M. Mudd agreed to delay the
construction of the Seeley W. Mudd

geology building she was donating in
memory of her husband, and allowed
the Institute to use the interest on that
donation to meet expenses.

The generosity of the Mudds to Cal-
tech is well known and evident. Funds
from Seeley G. Mudd built the Seeley
G. Mudd Geophysics and Planetary
Science Building. The Millikan Memo-
rial Library is also his gift. Both Har-
vey S. Mudd and Seeley G. Mudd served
as Trustees for many years.

What is not known is that the Mudds
also played a central role in the cre-
ation of the Kellogg Radiation Labora-
tory. It was natural for them to be-
come involved, for although the family
fortune was built on his father’s invest-
ments in copper and sulfur mines, See-
ley G. Mudd, after a brief try at mining
engineering at Columbia, took up medi-

“The world's largest x-ray, a gigantic tube operating under the impulse of 1,000,000 volts of

electricity, is being exhibited by scientists at the California Institute of Technology The ray,

which is being used in complicated scientific experiments, is so powerful that it will penetrate two
inches of lead, whereas a quarter of an inch of lead has heretofore stopped the most powerful X-
Ray ...” Photograph and text are from a Caltech press release. At the controls are Professors
Ralph D. Bennett and C. C. Lauritsen. (Photograph courtesy of the Archives, California Institute
of Technology). Figure 2

INSTITUTIONS OF PHYSICS

89

and raised horses for show. In the
space of a bit more than two weeks
there is an exchange of terse letters,
which can be paraphrased as follows:
3 March 1931
Kellogg to Millikan

Meet me at my ranch on Wednesday,
March 11.

15 March 1931
Kellogg to Millikan

I like your idea, but for $150 000 I
should have some appropriate ac-
knowledgment such as my name on
the building.

18 March 1931
Millikan to Kellogg

We can work out something.

21 March 1931
Millikan to Kellogg

The structure will be built and
equipped for about $120 000. An
additional $30 000 will endow its
maintenance. . . . the building to be
known as the W. K. Kellogg Radi-
ation Laboratory, and so inscribed in
the tablet to be placed in the center of
the east facade of the building.

22 March 1931
Kellogg to Millikan

I agree.

On 27 March 1931 the Pasadena
Star-News carried the following:
Foundation work was started this
morning at the California Institute of
Technology on the Radiological Labo-
ratory which is likely, according to
experts, to put Pasadena in the front
rank of the research centers in ra-
dioscopy and radiotherapy.

This must be one of the shortest
lapses of time known between a dona-
tion for a building and the beginning
of its construction. It gives the strong
impression that Kellogg became a
founder of the lab at the last minute.
It also appears that Millikan underes-
timated Kellogg’s potential as a donor.
Evidence for this is the fact that the
next year Kellogg donated his 700
acre horse ranch and $600 000, togeth-
er worth about $3 000 000 to the Uni-
versity of California. As you will see,
there is reason to think that for Milli-
kan this was “the big one that got
away,” and it bothered him all the
rest of his life.

But the laboratory was launched and
construction was rapid, although full
use of the x-ray equipment was held up
because the two 750 000 V transform-
ers were slow in coming from General
Electric in New York. When they did
come one had to be returned as faulty.
Still, the board of trustees approved the
budget of what Seeley G. Mudd called
“The Seeley W. Mudd X-Ray Research
Fund Program." Mudd was appointed
Research Associate in Radiation to ad-
minister the biology half of the pro-
gram. Figure 5 is a copy of his picture
in the 1933 Caltech yearbook “Big T”
which accompanied a description of his

work administering the treatment of
cancer patients in Kellogg. The first
patient was treated in the Kellogg Lab-
oratory in September of 1932. While
the laboratory was being readied, pa-
tients continued to be treated in High
Volts, as the adjacent High Tension
Laboratory was usually called.

Figure 6 shows the large interior
room of Kellogg laboratory. You can
see the thirty-foot long x-ray tube com-
ing down through the treatment
room. A rubber hose filled with water
was used as an electrical conductor to
carry the electric current from the
high-voltage transformer to the x-ray
tube. The potential drop was about
50 000 V. You can see the hose in the
photograph; the pie tins are corona
discs, which smooth the potential gradi-
ents. Often a spark would puncture

the hose and water would stream out. It
was the job of the physicists to keep the
tube in working condition, so a physics
graduate student would get into a bo-
sun’s chair and swing out to replace the
damaged section of hose.

In the treatment room (figure 7),
vestiges of which remain today, four
patients could be treated at a time, two
sitting and two lying down.

From 1931 until 1936 Kellogg was
devoted largely to radiation therapy,
but there was another life that flour-
ished among the “maintenance crew,”
the study of nuclear physics. Actually
most of this work went on in the adja-
cent High Volts building and was not,
strictly speaking, part of the Kellogg
laboratory.

In High Volts, Lauritsen and Crane,
reacting to the reports of Cockroft and

Graffito in recognition of Millikan’s activities as a fundraiser for Caltech (circa 1 937). Millikan was
a controversial and very public figure. (Photograph courtesy of the Archives, California Institute of
Technology.) Figure 3

90

HISTORY OF PHYSICS

Walton’s success, modified an x-ray
tube to accelerate ions. They produced
artificial radioactivity, and in January
1933 the Pasadena Star-News reported
that Lauritsen and Crane had produced
neutrons with an accelerator. They
used the reaction

Be9 + a— >C12 + n

and detected the neutrons by putting par-
affin linings into electroscopes invented
by Lauritsen for his x-ray work. This was
quite an accomplishment, considering
that James Chadwick had only reported
the discovery of the neutron a few
months earlier. The excitement of the
opening of an entire new field of research
captured most of the interest the physi-
cist might have had in x-rays for therapy.
Millikan and Lauritsen in their minds
had always kept the physics separate
from the cancer treatment. In the corre-
spondence eliciting support from physi-
cians and money from W. K. Kellogg, Mil-
likan seldom mentioned basic research,
but all the publicity releases were clear
on this point.

were clear on this point.

For example, the Los Angeles Times
of 4 August 1931 says
The largest and most powerful in-
strument ever devised for splitting
the atom and combatting cancer was
installed today in the California In-
stitute of Technology new radiation
laboratory. . . .

The primary object of the insti-
tute’s x-ray program, however, was
to learn about the physics of high-
speed electron particles.

And there was even a mention of the
possibility of producing nuclear disinte-
gration.

The doctors did cancer research; Cal-
tech did physics. Nevertheless, the X-Ray
Research Program supported Lauritsen
with part of his salary, with equipment,
and with postdocs and student assistants.
The Caltech High Potential X-Ray Re-
search expense sheets for 1934 show that
Millikan understood overhead — he knew
how to extract indirect costs from a grant
before the term was invented. A half doz-
en students were budgeted for the year —
among them one William A. Fowler —
along with two post docs and equipment
for “High Potential X-Ray Physics.”
Thus the “X-Ray Research Fund” paid
tuition for graduate students and sti-
pends for researchers who did nuclear
physics most of the time and kept the x-
ray tube running on the side.

Someone else’s money

For the first five years the lab was
supported by the money from Mrs.
Mudd, but as 1936 approached Milli-
kan had to search for more money for
the lab. Naturally enough he went
back to Kellogg, who aroused Milli-
kan’s hopes by holding out the prospect

Will Keith Kellogg of Battle Creek, Michigan
(circa 1928). (Courtesy of the W. K. Kellogg
Foundation). Figure 4

of a $3 000 000 gift to endow the lab.
These hopes launched Millikan and
Kellogg on a bizarre fund-raising effort.

The trouble was that Kellogg had
already given that money to someone
else. Kellogg proposed to retrieve his
$3 000 000 gift from the University of
California and give it to Caltech! He
was not happy with the way the Uni-
versity was running his horse farm; he
felt they had not lived up to the spirit of
the conditions he had placed on the gift
and that they should return it and its
endowment.

Millikan was realistic enough to fore-
see difficulties. He politely suggested
that Kellogg not tell the California
Regents that he was retrieving his
property in order to give it to Caltech.
Millikan also wanted his name left out
of any negotiations to reconvey the
property.

In December or 1936 Kellogg assert-
ed his claim to the Regents. He wanted
his gift back, he said, and went on
I have in mind the gift of this proper-
ty and endowment to California In-
stitute of Technology, a California
Corporation, primarily for the sup-
port of the Kellogg Radiological Lab-
oratory established about five years
ago and which is engaged in scientific
and medical research in the field of
radiology, particularly as applied to
the treatment of cancer.

The suggestion was coldly received,
and it provided meat for a wrangle that
went on for thirteen years.

The first year was exciting. Kellogg
marshalled his lawyers; Millikan ar-
rayed his trustees. Together they
probed the Regents. Millikan and Uni-
versity of California President Robert
Gordon Sproul jousted politely, Sproul

holding out hopes but giving nothing
away. When rumor came that only
one particular Regent, a devout Catho-
lic, was the focus of opposition, Milli-
kan visited Archbishop Cantwell and
asked him to intercede. The Archbish-
op sent back the message that the
board was “unanimous in its opposition
to the transfer.” They tried to use
Herbert Hoover’s influence, but to no
avail. Kellogg even suggested to Cal-
tech trustee Harry Chandler, publisher
of the Los Angeles Times , ”... a short
program which if carried on in the
proper way through newspapers, might
have some effect on the Regents. . .” but
nothing came of it.

Kellogg donated $10 000 to keep the
lab going for another six months, but
after seven months of failing to get
back his gift from the University of
California, his spirits sank. Millikan
tried to rally them in a long letter:

. . . the transmutation of the ele-
ments, now an accomplished fact,
plus artificial radioactivity, plus neu-
tron beams — all three effects produc-
ible by Lauritsen tubes — plus the
manifold uses of ultra-short wireless
waves, therapeutic and otherwise,
open up endless opportunities which
with the addition of brains, persis-
tence, energy and some financing
should keep the Kellogg Radiation
Laboratory for many years to come
as it has been for the past six years an
unexcelled center of physical and
biological progress, exerting perhaps,
as beneficent and as far-reaching an
influence as any activity of the Kel-
logg Foundation.

This is one of the few times that
Millikan is so explicit to Kellogg about
the nuclear physics that went on in the
lab in parallel with x-ray treatments.
He concluded by suggesting that Kel-
logg simply endow the lab from his own
money and work out the details of
retrieving his property from the Uni-
versity of California later. Without
additional operating funds, Millikan
declared the lab would cease to operate
on 1 November 1937.

Millikan’s urgency is even more evi-
dent in his suggestion to the Caltech
trustees that they negotiate some sort
of compromise with the Regents:

It isn’t merely the cancer work that
is at stake, it is the whole of Laurit-
sen’s nuclear physics work which is
as important as anything being done
now in the country.

In fact, there was some reason to
hope for compromise. The gift to the
University of California required that
the Arabians be bred and shown for-
ever, but the endowment did not cover
the costs. The ranch was a drain on
the University budget, and it seems
that Sproul was willing to return part
of the gift in return for unrestricted use
of the remainder. The Regents, howev-

INSTITUTIONS OF PHYSICS

91

er, foresaw the long-term value of land
in Southern California; besides, they
were not about to do Caltech any fa-
vors. After all, if Kellogg was so inter-
ested in radiation laboratories, they
had one of their own at Berkeley; let
him shift his gift there.

In October of 1937 Millikan admitted
to Kellogg’s lawyer that the prospect of
reconveyance of the land looked hope-
less. As he wrote a few months later to
Kellogg

So far as my own activities are con-
cerned, I have been virtually in-
formed by one of the regents of the
University of California that it would
be wise for me personally to forget it.

The end of cancer research

It was time to open a new approach to
funding the laboratory. Millikan went
back to a traditional Caltech method.
Find the best person available in the
field, lure him to Pasadena for the win-
ter, impress him with the quality of work
at Caltech, and then use his reputation to
garner further support. So with $5000
from Kellogg, Millikan and Lauritsen
brought the eminent French radiologist
Henri Coutard to Caltech.

Millikan now began to explore fund-
ing from the National Cancer Advisory
Council of the National Academy of
Sciences. He wrote to Dr. Ludvig Hek-
toen, the program’s director, selling the
need for studies of radiation therapy.
Then, with some encouragement from
Hektoen, Millikan drew up a proposal.
Heavily using Coutard’s name, Milli-
kan asked for $62 500.

In the meantime Millikan went back
to Kellogg. Almost 78 years old and in
the throes of a series of operations for
glaucoma, which left him blind for the
remaining 13 years of his life, Kellogg
was occasionally a bit testy at Milli-
kan’s importunings. He complained of
the more than $2000 in legal fees in the
fruitless effort to retrieve the gift from
the University of California; he men-
tioned his painful and unsuccessful eye
operations; he asked Millikan to leave
him alone; and in January 1938 he
wrote, “I am not prepared to commit
myself for any further contribution
toward the x-ray laboratory for the
present year.”

Millikan, imperturbable as ever,
thanked him for his generosity, told of
his efforts with Hektoen and promised
to press on. But in February the pro-
posal to the National Cancer Advisory
Council was rejected. Some of the
reasons for the rejection surely had to
do with the growing recognition that x-
ray therapy was not very effective.

The pathologist associated with the
Kellogg Lab had written a report to
Hektoen that seemed to show the treat-
ments did little good and may have
done harm:

Seeley G. Mudd in his office in the Kellogg
Radiation Laboratory, about 1933. (Photo-
graph courtesy of the Archives, California
Institute of Technology). Figure 5

I have no evidence in any material
that any case of prostatic carcinoma
has been destroyed by radiation ther-
apy. There have been a few cases
where no tumor was found at autopsy
but there was profound necrosis in
the prostate, apparently following
radiation and trans-urethral resec-
tion, involving the entire organ so
that no viable tissue remained. . . .
Intense fibrosis has been produced in
many of the cases and perhaps in
some this has been very excessive —
to the detriment of the patient. This
particularly happened in the first
years when the matter of dosage and
length and number of exposures was
not as well worked out as at pre-
sent. . .

We have had much happier results
in cervical carcinoma. We have had
a few cases from whom we took
repeated biopsies and have seen all
the stages of cellular disintegration
and destruction of cells as described
by those who have used radium and
200 kV x-ray. ... At the same time
we have had plenty of cases where
the tumor has progressed in spite of
our attempts to destroy it. . . . How-
ever, I see only the dead cases repre-
senting the mistakes, failures and
disappointments. The palliation
that many patients get, the prolonga-
tion of life and other factors which
our clinicians believe occur in a large
number of patients, I do not see.
The tone of the pathologist’s report of
the results of seven years of research
could hardly have been persuasive to
Hektoen. But Millikan did not give
up. He next went to the recently
endowed Childs Foundation at Yale
and prepared to approach the DuPont

family and to try Kellogg again.

But then came a change that spelled
the end of the program of cancer treat-
ment. Seeley G. Mudd, now Professor
of Radiation Therapy, had served the
project since it began. He saw the
research as played out, and in April he
wrote to Millikan, then in the East, to
ask him to find a replacement,

... a highly competent and conserva-
tively minded roentgen therapist to
sit on the lid at Kellogg and keep the
clinic running smoothly.

... You will recall that I am at-
tracted to the biological and chemical
angle in cancer research more than
to attempt to make minor modifica-
tions in the existing therapeutic
techniques using supervoltage irra-
diation.

After the rejection of his proposal by
the Childs Fund in mid-May, Millikan
had only one hope left. He went back
to W. K. Kellogg. He wrote a long
letter regretting the stubbornness of
the Regents and sadly informing Kel-
logg that the lab would have to close on
June 30. He recapitulated the accom-
plishments of the program but gave his
description a twist that showed he had
accepted the end of Seeley Mudd’s Sup-
port of the program.

Over seven years the program had
cost about $1500 a month, Millikan told
Kellogg. ‘‘Rather more than half of
this had been required for the direct
cancer treatment program, ...” But
for the future

Dr. Lauritsen’s part, which has con-
sisted in the development of the new
physical techniques, must not be dis-
continued, and I am making vigorous
efforts to find means of helping him
at his present promising activities in
the development of new radio-active
elements and other nuclear physical
problems, which have good prospects
of extending still further the benefi-
cent effects of radiation in the treat-
ment of cancer and other human
ills. He has just built a new tube
which should be capable of working
at two and a half million volts, and
this tube in the hands of himself and
his pupils, is pretty certain to open
up new results in the field of nuclear
disintegrations and atomic transfor-
mations, all of which are promising
for the future of radiation therapy in
the broad sense.

The ‘‘future of radiation therapy in
the broad sense” is the precursor an-
nouncement of the change then under
way in the Kellogg Radiation Laborato-
ry. There is a certain lack of candor in
referring to the 2-MV Van de Graaff as
a “tube” as though it were just a
further development of Lauritsen’s x-
ray work, but there is real ingenuity in
presenting the study of the structure of
light nuclei as promising for radiation
therapy “in the broad sense,” because

92

HISTORY OF PHYSICS

strictly speaking it was true.

On 1 June Kellogg responded gener-
ously, asking Millikan if $10 000 would
keep the lab going for another year. We
can only speculate what would have
happened if Kellogg had offered the
$18 000-20 000 needed to maintain the
full program. Or what the lab would
be like today if the Childs Fund or the
National Academcy of Sciences had
supported Millikan’s program. Kel-
logg’s partial offer, however, allowed
Millikan a graceful exit from the treat-
ment program.

His 9 June 1938 reply to Kellogg is
Millikan at his best. With $10 000
they could only support part of the
program. Dr. Mudd would complete a
statistical study of the nearly 800 cases
already treated.

Dr. Lauritsen and his group, on the
other hand, are eager to push up to
higher potentials by new techniques
with the aid of which there is the
possibility that new radioactive sub-
stances may be artificially pro-
duced. If successful, this procedure
may make the use of very penetrat-
ing rays much cheaper and vastly
more convenient than it is when the
patient must be brought to some
point at which an expensive high
potential tube exists. We propose
then, on July 1st, to discontinue the
use of the present tube for the time
being and build, in the big room of
the Kellogg Laboratory, a modified
tube which will go to considerably
higher potentials.

Depending on how things worked
out, treatments might be resumed later
with the new tube or the old. (And
again there is a certain disingenuous-
ness in Millikan’s description of the
Van de Graaff as a “modified tube.”)

With unusual precision, then, we
have dated the moment when the can-
cer treatment research was recognized
as played out and the nuclear research
that had been burgeoning on the pe-
riphery of Kellogg took over. The labo-
ratory’s destiny now lay firmly in the
hands of the physicists.

Epilog

This would be the point to go back
and trace the history of the nuclear
physics that built the lab’s worldwide
reputation, but that fascinating story is
for another chapter. Instead, we will
tie up some loose ends by detailing the
rest of Kellogg’s contributions to the
lab and telling what became of his
project to give to Caltech what he had
already given to the University of Cali-
fornia.

In 1939 Millikan and Mudd visited
Kellogg and reported the work of the
lab. Kellogg offered $8000 that year,
but announced to Millikan that the
money was to be considered his last
contribution to the program.

The central hall of the Kellogg Radiation
Laboratory in 1 933. Inside the cement balcony
in the middle of the photograph is the treat-
ment room, shown in figure 7. (Photograph
courtesy of the Archives, California Institute of
Technology). Figure 6

But Millikan would never give up. A
year later he sent a detailed report to
Kellogg on the uses of the money.
Acknowledging that the previous
year’s donation was to be Kellogg’s last,
Millikan asked him to suggest a new
"friend” for the lab. Kellogg suggested
the Kellogg Foundation, which, after a
visit by Millikan to Battle Creek, gave
$8000.

In 1941 there was another attempt to
make a deal with the University of
California. A fifty-fifty split was of-
fered. President Sproul had a stormy
session with Kellogg, who later wrote
to Millikan

I regret the outcome of this contro-

versy, but hope that at some future
time Dr. Sproul and his Regents will
"see the light” and be willing to
share this property with Cal Tech.
Emory Morris, the President of the
Kellogg Foundation, washed his hands
of the business.

Throughout 1940 and 1941 the na-
tion was mobilizing for war. The
changes at Kellogg Lab were dramatic
as the lab became a major design and
production center for rockets. Laurit-
sen headed a rocket project staff of
more than 3000. How completely the
lab had become a government facility
was lost on Morris who in 1942, on
behalf of the Kellogg Foundation,
asked for a progress report on the use of
the $8000 and offered more.

Millikan’s reply is interesting. All
the justifications for the support of
research reduce to three: Support re-
search for its useful applications; sup-
port research for the love of knowledge;
support research because the people
who do it are a valuable resource to be
cultivated for a time of need. In all his
dealings with Kellogg, Millikan had
hammered home the theme of useful
applications. Only rarely did he allude
to the marvelous discoveries that were
being made at the laboratory. Only by
implication did he advocate support of
Lauritsen for his unique qualities as a
scientist.

Now, however, with the war on, the
value of these physicists as a national
resource was clear. In his response to
Morris he developed the theme:

The outstanding place which that
laboratory has taken during the past
twelve years has been practically
wholly due to the extraordinary ef-
fectiveness of Charles C. Lauritsen
and his very able collaborator, Wil-
liam Fowler. My main concern in all
my talks during the last half dozen
years with Mr. Kellogg and the offi-
cers of the Foundation has been to
arrange conditions such that this
team could be kept working at maxi-
mum efficiency. . . .

No matter what sort of jobs are
assigned to them, a team of the Laur-
itsen-Fowler type is a great rarity,
and it is a great credit to the laborato-
ry that it has produced and main-
tained them.

The widespread acceptance of this
approach after World War II led to the
federal support of science on a scale
never previously imagined. Millikan,
with characteristic intuition, had
grasped the central argument that
would dominate postwar science.

Although the Foundation under
Morris’ leadership donated $15 000 to
the laboratory in 1942, Millikan had no
similar success after the war. Morris
finally called a halt to Millikan’s ef-
forts in 1948 by writing
If the W. K. Kellogg name on the

INSTITUTIONS OF PHYSICS

93

The x-ray treatment room in the Kellogg Radiation Laboratory around 1932. The x rays were
generated when electrons from a filament in the base of the tube (below the treatment room)
struck a target placed at the level of the tube portals (seen in the center of the photograph). Four
patients could be treated at one time. (Photograph courtesy of the Archives, California Institute
of Technology). Figure 7

laboratory is going to jeopardize in
any way the future support of the
laboratory there should be no hesi-
tancy on your part in removing the
name on the laboratory in favor of
any individual who would desire to
create an endowment to perpetuate
the work you are doing. I have
conferred with Mr. Kellogg on this
matter and he concurrs [sic] with this
opinion.

Millikan made one last try. He kept
up his annual visits to Kellogg. The two
octogenarians would meet each year at
Palm Springs where Kellogg now win-
tered. Millikan would report to him

the activities of the laboratory and they
would discuss more cosmic philosophical
matters. It was through such contacts
that Millikan learned that he had one
more chance at the Kellogg Ranch.

In 1943 Kellogg had sent Millikan a
copy of a letter from Henry L. Stimson,
Secretary of War. The letter thanked
Kellogg for arranging the donation of
the Pomona ranch to the Army. “The
gift will be a great asset to the Army
horsebreeding plan.” In return for
donating the ranch to the Army, the
University of California received clear
title to the ranch’s endowment. The
University of California and Kellogg,

under the goad of patriotism, had final-
ly come to an agreement.

After the war the government put
the ranch up for sale. Kellogg was
outraged at this violation of his gener-
osity. His complaints and petitions
from influential friends persuaded the
government to give the ranch to the W.
K. Kellogg Foundation.

Millikan learned of these events
after a visit with Kellogg in early
1949. Writing to Morris of his visit
with Kellogg, Millikan said

He asked me particularly to drop
you a note to suggest that if the
Kellogg farm, which is now reported
as being turned back to the Founda-
tion and has the possibility of being
given by the Foundation to some
philanthropic institution, the Cali-
fornia Institute of Technology
should, in view of past history, have
first place in the picture.

Kellogg had deliberately minimized
his influence with the Foundation from
its start in 1930. By this time it was
nil. The Foundation gave the land to
be the Pomona campus of the Califor-
nia Polytechnic State University. To-
day Cal Poly breeds and shows the
Arabian horses descended from Kel-
logg’s original herd on the land that
despite Millikan’s Herculean efforts
never became Caltech’s.

* * *

With a few exceptions all the quoted materi-
als in this article are from the Robert A.
Millikan papers in the Archives of the Cali-
fornia Institute of Technology. I appreciate
the easy access to these papers and photos,
which have been brought to a high state of
organization under the leadership of the
Institute's Archivist, Dr. Judith Goodstein. I
am especially grateful for the help of Dr.
Goodstein’s assistants Susan Trauger and
Carol Finermann.

94

HISTORY OF PHYSICS

the

evolution
of the

Office of Naval Research

By The Bird Dogs

IT is not often that the birth of a Navy office, which
certainly sounds like like a cold, administrative af-
fair, makes history worth recording. But the birth
of the Office of Naval Research was such an interesting
one, participated in by so many famous and brilliant
personalities, that a record of the events should serve
a useful purpose. It might even bring inspiration to
those who daily continue the struggle to evolve con-
structive changes in large government departments.

Soon the Office of Naval Research (ONR) will be
celebrating its fifteenth anniversary. If the celebration
is anything like the tenth reunion affair, a banquet will
be held and a number of speeches will be made extolling
the aims, purposes, and accomplishments of this re-
markable office. Included will probably be a few re-
marks concerning the history of the formation of ONR.

Any reference to the history of ONR excites in the
authors two responsive chords. The first is one of nos-
talgia brought on by fond and fascinating memories.
The second is one of frustration caused by the realiza-
tion that an authoritative history of the evolution of
ONR has not, heretofore, been made public. Hence this
attempt.

The campaign to sell the concept of establishing a
central office to foster basic research and research co-
ordination within the Navy Department was a lengthy,
and sometimes bloody, struggle. The story of the evolu-
tion of ONR is really the tale of an educational process
carried on over a five-year span (providing we are per-
mitted to ignore pre-World-War-II struggles). This edu-
cational process required the concerted efforts of many
people to create an atmosphere in the Navy Depart-
ment, in the Executive Branch, and in Congress, which
was favorable toward long-range research. Key people
had to be convinced that future military strength de-
pends to an increasing degree on the rapid and effec-
tive development of new weapons and weapons systems
through a strong, balanced research effort.

It is recognized that history must be recorded from
several points of view before all the facts are exposed.
The story here presented was that as seen by a small

PHYSICS TODAY / AUGUST 1961

group of Naval Reserve officers who were fortunate
enough to have had a five-year worm’s-eye view of the
entire evolution of ONR from a vantage point within
the Office of the Secretary of Navy. We were, in the
parlance of the day, lowly skippers of LSD’s (Large
Steel Desks).

The Background

TT all began before the United States entered World
A War II, with the realization by such outstanding
men of science as V. Bush, J. B. Conant, K. T. Comp-
ton, and F. B. Jewett, that this country was woefully
weak in military research and development. Dr. Bush
carried the idea of establishing a National Defense Re-
search Committee “to coordinate, supervise, and con-
duct scientific research on the problems underlying the
development, production, and use of mechanisms and
devices of warfare (except problems of flight which
were to remain under the NACA)” to President Frank-
lin D. Roosevelt and Mr. Harry Hopkins early in June
1940. The White House acted rapidly and on June 15,
1940, the President signed letters appointing such a
Committee with Dr. Bush as chairman. The Committee
was to supplement rather than replace the activities of
the military services so that links with the military were
formed by the naming, as members, Brig. Gen. G. V.
Strong of the Army and Rear Adm. H. G. Bowen of
the Navy, in addition to K. T. Compton, J. B. Conant,
F. B. Jewett, R. C. Tolman, I. Stewart, and C. P. Coe.’

To further mobilize the scientific personnel and re-
sources of the nation, President Roosevelt established
by Executive Order on June 28, 1941, the Office of Sci-
entific Research and Development. This group had as
an Advisory Council Dr. Bush as Chairman, Dr. Conant,
Chairman of the NDRC, Dr. J. C. Hunsaker, Chairman
of the NACA, Dr. A. N. Richards, Chairman of the
Committee on Medical Research, and one representa-
tive each from the Army and Navy appointed by the
respective Secretaries.

The impact of this move led Secretary of Navy Frank

INSTITUTIONS OF PHYSICS

95

A recent photograph of several of those who took part in the early development of ONR. (The names of the original and
second-wave “bird dogs” are italicized.) Front row, left to right: Bruce S. Old, Ralph A. Krause, R. Adm. Julius A.
Furer, USN (Ret.), Jerome C. Fiunsaker, James H. Wakelirt. Back row: N. S. Bartow, Royal C. Bryant, John T. Burwell,
H. Gordon Dyke, A. C. Body, Thomas C. Wilson, James P. Parker. The principal author of the present article is Dr. Old,
who is now senior vice president of Arthur D. Little, Inc., Cambridge, Mass.

Knox to study what steps the Navy might take to in-
crease its effectiveness in the prosecution and utiliza-
tion of research and development.

There existed some controversy on this point. Rear
Adm. H. G. Bowen, Director of the Naval Research
Laboratory, had recommended on January 29, 1941,
the centering of all research for the Navy in that Labo-
ratory, giving it Bureau status; whereas the General
Board in a rebuttal on March 22, 1941 had recom-
mended that no change in Bureau cognizance for re-
search be made and that the Chief of Naval Operations
be made responsible for all research policies, including
the operation of the Naval Research Laboratory.

Secretary Knox, at the suggestion of Rear Adm. J. H.
Towers, therefore enlisted Prof. J. C. Hunsaker, the
Chairman of the NACA as well as a member of the
OSRD, and a graduate of the Naval Academy, to ad-
vise him. Out of this advice arose the first step in the
long road to ONR. At the suggestion of Hunsaker, Knox
issued General Order 150, July 12, 1941, which estab-
lished the Office of the Coordinator of Research and
Development in the Office of the Secretary of the Navy.
This order provided that the Coordinator advise the
Secretary broadly on matters of Naval research, and
placed the Naval Research Laboratory under the cog-
nizance of the Bureau of Ships.

The Office of the Coordinator of R & D

AT the urgent request of Secretary Knox, Dr. Hun-
saker agreed to serve as the first Coordinator of
Research and Development on an interim basis in or-
der to get the Office organized and functioning. He was
named Coordinator on July 15, 1941, and immediately

selected a small staff consisting of two highly capable
regular officers, Capt. Lybrand P. Smith and Comdr.
E. W. Sylvester, and four young Naval Reserve offi-
cers having technical backgrounds. Hunsaker then pro-
ceeded to inspire these young men, whom he called
“bird dogs,” and train us in his effective manner in the
basic elements of sound research program planning, ad-
ministration, evaluation, and coordination. Another im-
portant facet of this training concerned the ways and
means of getting things accomplished in wartime Wash-
ington in the face of odds, or even open opposition.
With tongue in cheek, Hunsaker often asked the “bird
dogs” to investigate situations and prepare brief memo-
randa. These he then waved around in the stratospheric
secretarial or bureau-chief level to show that his posi-
tion was obviously correct if even green reserve officers
could quickly reach the same conclusion. (This pro-
cedure had a remarkable effect on the care with which
memoranda were prepared, and on the morale of the
staff through the display of confidence it represented.)

In order to carry out more efficiently his prior com-
mitments to the NACA and OSRD, Hunsaker resigned
the position of coordinator and turned it over to his
carefully selected choice, Rear Adm. J. A. Furer, USN,
on December 15, 1941. However, Hunsaker’s superb
advice and counsel always were, and at this w'riting still
are, available to and continually utilized by the Navy
Department. Other changes included the naming of
Furer to the OSRD, Smith to the NDRC, the acqui-
sition of Comdr. R. D. Conrad, USN, a truly brilliant
technical man, as a replacement for Sylvester, and the
addition of twm more technical Naval Reserve officers.

During the first three years of World War II the
work of this Office was aimed almost entirely at liaison

96

HISTORY OF PHYSICS

between the NDRC and the Navy, assisting in the plan-
ning and establishment of research projects, following
the progress thereof, and aiding in bringing about the
utilization of the results by the Navy. (The effective-
ness of this work under Adm. Furer’s guidance is noted
by J. P. Baxter in his history of the OSRD and NDRC
entitled Scientists Against Time.) In addition, the Office
coordinated Navy research efforts with the War De-
partment, War Production Board, Coast Guard, Na-
tional Advisory Committee for Aeronautics, National
Research Council, and the United Kingdom and Canada.

However, from the very outset another important
subject occupied the thoughts of the personnel of the
Office of the Coordinator of Research and Develop-
ment. All of us knew that the excellent OSRD-NDRC
civilian research groups would probably evaporate as
soon as the war ended. Therefore, at each step of the
way, a gnawing thought occupied the minds of all: how
could the Navy better organize and administer its own
research? The Navy must be capable of developing the
impressive and awful strength required to discourage
any potential enemy to the end that the Navy could
assist in avoiding further wars, or, at a minimum, avoid
entering any future war without having all the advan-
tages effective research could provide in modern weap-
ons and weapons systems. Hunsaker sparked this think-
ing in 1941 within a matter of days after establishing
the Office. One of the first tasks he assigned the group
was a study of various Navy laboratories in order to
determine wherein the Navy might be able to handle
research work effectively so as to lessen the burden of
the NDRC, and to determine wherein its research ca-
pabilities were lacking.

A searching analysis of Navy research strengths and
weaknesses was actually a continuous task which came
into consideration in practically all the work of the
Coordinator's Office. In establishing liaison with the
Bureaus, Offices, and Laboratories of the Navy Depart-
ment, and in naming Navy liaison officers to the nu-
merous NDRC projects, a rapid evaluation of the atti-
tudes and capabilities of people was obtained — whether
they w'ere civil service, ensigns, or admirals. In a re-
markably short time it w'as possible to categorize those
persons who would do everything possible to stimulate
better research programs, organization, and utilization
of results, and those who stood firm upon the twin, and
usually backward, defenses of cognizance and entangling
red tape.

Fortunately within the Navy there arose almost im-
mediately a solid core of highly intelligent people who
welcomed and assisted the drive to push research on all
frontiers. This was in part a tribute to the well-estab-
lished Navy system of postgraduate study in various
universities W'hich had developed in many officers an
understanding and appreciation of science.

This is not to say that all W'as peaches and cream.
Well do we remember the time early in the war when
we called in a top submarine officer and pointed out to
him the magnitude of the US and UK antisubmarine

research effort. We postulated that the enemy was also
doing work and out of it would come developments, like
a homing torpedo, which would make life miserable for
the submarines. Would he help us spark some pro-sub-
marine research? Absolutely not— the subs in the Pa-
cific w'ere having a field day. This type of short-sighted
thinking we paid for dearly later. We also remember
probing into touchy areas, such as out-dated torpedo
pow'er plants, only to have officers rise in indignation
based on rights of cognizance or secrecy. In fact, we
had to develop a defense technique. Whenever we ran
into a particularly salty, operational type who was bel-
lowing in a manner destined to hold up the progress of
research, we took out notebook and pencil and asked
dutifully, “Would you mind repeating that statement
so I could be certain to quote you correctly to the Co-
ordinator of Research? He will be interested in your
view, sir." This technique worked wonders.

We continually sought out and nurtured the progres-
sive, intelligent core group. One of the first persons to
be uncovered who show'ed vital interest in the postwar
reorganization of research in the Navy was George B.
Karelitz of Columbia University, a former Russian,
who was working with the Bureau of Ships.

Two of the “bird dogs” began in 1942 to meet bi-
monthly at home in the evening with Karelitz. Tragi-
cally, Prof. Karelitz died in 1943, but fortunately not
before he contributed immensely to the shape of things
to come. Out of these sessions the initial pattern of
ONR was almost completely conceived — the essential
elements consisting of establishing a central research
office in the Office of Secretary of the Navy, headed by
an admiral, receiving funds from Congress for research
projects, and having a powerful research advisory com-
mittee made up of top scientists, were actually all
drawm up and recorded as early as November 1, 1943
by two “bird dogs.” Of course much ground work in-
volving numerous persons both within and outside of
the Navy remained to be accomplished before any such
plan could become a reality.

Since any research organization requires a sympa-
thetic atmosphere in w'hich to live, if it is to survive
and be productive, the work of a large number of peo-
ple during the first three years of World War II must
be credited for setting the stage in the Navy Depart-
ment for the later establishment of a central research
office. Among the scientists who helped so materially in
“selling” the importance of continued research to the
Navy during this time were: Bush, Conant, Compton,
Jewett, DuBridge, Adams, Rabi, Tuve, Tolman, Hun-
saker, Terman, Loomis, Tate, Zacharias, Hunt, Kistia-
kowsky, Lauritsen, Morse, Stevenson, Suits, Ridenhour,
Alvarez, Land, Kelley, Buckley, and Wilson.

And among those most receptive officers in the Navy
Department wffio w'ere sold and in turn helped to pre-
pare the Navy for subsequent reorganization were:
Briscoe, Bowen, Furer, L. Smith, Solberg, McDowell,
Tyler, Schuyler, Entwisle, Bennett, Sylvester, Conrad,
Lee, Hull, Dowd, Baker, Low, Cochrane, Mills, In-

INSTITUTIONS OF PHYSICS

97

gram, Rickover, Piore, Bollay, Thach, de Florez,
Strauss, Berkner, Teller, Lockwood, Kleinschmidt,
Hatcher, Pryor, and Schade.

Certain official acts also occurred which spread the
word on research in a fairly effective manner to the
various Bureaus and Offices of the Navy Department.
One mechanism was the establishment of the Naval Re-
search and Development Board, headed by Furer, which
consisted of the various Bureau research heads and
the Readiness Division of Cominch, and had a “bird
dog” as secretary. An interesting aspect of this work
which soon arose was the need for better technical in-
telligence in order to aid in the rapid development of
countermeasures to new enemy weapons. A new group
was quickly established in the Coordinator’s Office with
two additional “bird dogs” to assist in this important
work, and liaison was established with the Office of
Naval Intelligence, G2 of the Army, and the Office of
Strategic Services. The group performed outstanding
work in piecing together data on German torpedo, ram
jet, and guided missile work which resulted in the initia-
tion of important new projects in the US. Out of this
grew an awakening in the Navy to the important part
scientists could play in intelligence. As a result the
Navy sent one of the “bird dogs” on the first famous
Alsos Mission, and later set up the highly successful
Navy technical intelligence mission to Europe.

Plans for the Postwar Era

TOECOGNIZING fully the almost total dependence
of the Navy on NDRC research at this time, Rear
Adm. Furer, as early as the fall of 1943, began to worry
about what would happen to research in the Navy if the
war suddenly ended. The first trial balloon was hoisted
by him September 22, 1943, when he sent a memoran-
dum to Vice Adm. F. J. Horne, Vice Chief of Naval
Operations, suggesting a revision of General Order ISO
giving a few expanded coordinating powers (but no
money) to the Office of the Coordinator of Research
and Development. Also he proposed that the Naval Re-
search Laboratory be transferred back to the Secre-
tary’s Office. In this memo Furer invented the term
“Chief of Naval Research” which was ultimately
adopted as the title for the head of ONR. However,
at this time the several Bureaus raised a large howl
based on cognizance, and Admiral King was in no mood
to favor any more power in the Secretary’s Office, so
the whole matter was dropped like a lead balloon.

Other factions were also beginning to awake. Mr.
James Forrestal, Under Secretary of the Navy, on Oc-
tober 2, 1943 requested R. J. Dearborn, President of
Texaco Development Corporation, to “make an exten-
sive survey of Navy patent practices and the research
situation of the Navy.” Mr. Dearborn reported his find-
ings on March 10, 1944 in which he recommended the
“establishment of an Office of Patents and Research to
be headed by a Coordinator of Patents and Research
(which does not conflict with the present activities of

the Coordinator of Research).” Mr. Forrestal was re-
luctant to take immediate action.

The Pot Begins to Boil

BUT, the lid could not be kept on the pot much
longer. Dr. Bush warned the military members of
the OSRD Advisory Council in the Spring of 1944 that,
“The OSRD is a temporary war organization which au-
tomatically goes out of existence at the end of this war;
so that in planning for peacetime research and develop-
ment, we plan without that organization, which will pre-
sumably turn its affairs over just as soon as the war
begins to end.” This official warning note was a loud
reminder that the scientists would in all probability
flock back to their own laboratories as soon as the war
appeared to be definitely won.

Furer immediately got busy and organized a large
conference in the Navy Department on April 26, 1944,
to discuss the problem. To this conference were invited
all the top Army, Navy, and OSRD research personnel,
some 43 in number. There was general agreement that
the military would probably not be able to retain the
interest of top scientists or obtain funds necessary for
a vigorous research program. It was decided a commit-
tee should be established to study and recommend a
proper organization for postwar military research. In
retrospect, one of the most important points of the en-
tire conference was one of omission. Not one person in
the course of the meeting hinted in any way about the
tremendous revolution soon to be thrust upon military
research requirements by the advent of guided missiles,
complex weapons systems, and the like.

As a consequence of this meeting Secretaries Stimson
and Forrestal appointed a Committee on Post-War Re-
search composed of Charles E. Wilson, chairman, four
civilian scientists (Jewett, Hunsaker, Compton, and
Tuve), four representatives of the War Department
(Echols, Waldrin, Tompkins, and Osborne), four rep-
resentatives of the Navy Department (Furer, Coch-
rane, Hussey, and Ramsey), and two secretaries, in-
cluding one of the “bird dogs”. At the first meeting on
June 22, 1944, Chairman Wilson read to the press and
news reels the following statement:

The purpose of the Committee is to prepare a plan
and organizational procedure which will insure the con-
tinued interest of civilian scientists after the war in
scientific research for the Army and the Navy. The
nation’s scientists have been doing a splendid job since
Pearl Harbor, and our task is to evolve a plan which
will assure their continued interest in meeting the re-
search needs of our Armed Forces after the War. In
this way only can the United States keep ahead of all
possible future aggressors in preparedness for National
Defense.

The often heated deliberations of this committee
finally resulted in the recommendation (drafted by
Hunsaker) that an interim organization be established
in view of the fact that Congress was considering sev-
eral bills to create a new independent research agency

98

HISTORY OF PHYSICS

The first meeting (June 22, 1944) of the Committee on Post-War Research. Those
present, left to right, were Col. R. M. Osborne, R. Adm. G. F. Hussey, Jr., K. T.
Compton, Brig. Gen. W. F. Tompkins, R. Adm. J. A. Furer, F. B. Jewett, Charles
E. Wilson, J. C. Hunsaker, Maj. Gen. 0. P. Echols, R. Adm. E. L. Cochrane, M.
A. Tuve, Maj. Gen. A. W. Waldon, and R. Adm. D. C. Ramsey. US Navy photo

to which the functions of the interim organization might
better be transferred later. Accordingly, in a joint let-
ter on November 9, 1944, Secretaries Stimson and For-
restal requested the National Academy of Sciences to
establish the Research Board for National Security.
F. B. Jewett, President of the Academy, proceeded im-
mediately to organize the Board under the chairman-
ship of K. T. Compton. The Navy assisted materially
in getting the RBNS organized and' projects established
with R. Adm. Furer taking the lead and the “bird dogs”
helping in various secretarial and committee tasks.
However, the RBNS was destined to enjoy but a brief
existence, as President Roosevelt directed the Secre-
taries of War and Navy in March 1945 (with Bureau
Of the Budget urging) not to transfer funds for the use
of RBNS pending a thorough review of the several bills
before Congress for the organization of postwar re-
search. The RBNS was finally killed by a joint letter
from Secretaries Patterson and Forrestal dated October
18, 1945. Despite its short life the ill-fated RBNS
served a very useful role in educating top people in the
military services and Congress, thus preparing the way
for more successful future actions on research organi-
zation.

In the period between the birth and death of the
RBNS things were moving rapidly on other fronts.

In the summer of 1944 the “bird dogs”, stimulated
by the work of the Committee on Post-War Research,
further developed their plan for a Navy office to key
in with whatever outside agency Congress might estab-
lish. It was on September 6, 1944, that two of the “bird
dogs” first set down a new organization chart for an
Office of Naval Research which entailed the naming of

an Assistant Secretary of the Navy for Research with
broad powers, an Advisory Committee, a Rear Adm.
Chief of Naval Research, program emphasis on basic
research work, and the transfer of the Naval Research
Laboratory to the Office. This was a vitally important
improvement over their earlier plan which had called
for a rear admiral as head of the Office. This plan for
an Assistant Secretary of the Navy for Research was
discussed with Dr. Hunsaker and Dr. Bush who en-
thusiastically supported the idea. The whole scheme
was then recorded by three of the “bird dogs” on Sep-
tember 23, 1944 as a beneficial suggestion to the Secre-
tary of the Navy. But this mechanism was not needed,
as Adm. Furer, Capt. Smith and Capt. Conrad all
quickly endorsed the thought. Thus, Adm. Furer sent
a memorandum to the Secretary of the Navy on Oc-
tober 11, 1944, recommending immediate implementa-
tion of such a move.

This was received coldly by Mr. Forrestal, who was
considering only one new Assistant Secretary, and had
him pegged in the field of supplies and logistics. Also
he w'as about to spring a surprise which wmuld soon
lead to the replacement of Adm. Furer. In just eight
days, on October 19, 1944, he established the Office of
Patents and Inventions, with Vice Adm. Bowen in
charge, as a first step in implementing the previously
mentioned Dearborn report. This was followed by a
series of moves which made it obvious that another
change was coming.

This maneuvering became of concern to the “bird
dogs” as we thought it might ruin our plans for an ef-
fective postwar organization. An incident which oc-
curred caused us to take a rather desperate chance. By

INSTITUTIONS OF PHYSICS

99

happenstance we came into possession of a comment
made by President Roosevelt on a fat report by Adm.
E. J. King concerning a suggested postwar reorganiza-
tion of the Navy Department. The terse comment, hand-
written on the cover, went something like this: “Ernie
—I made you Cominch to fight the war, not to reor-
ganize the Navy Department — FDR.” This made it
painfully clear that the President intended to control
postwar departmental changes. We believed so strongly
in our method of organizing research in the postwar
Navy that we decided to take the risk of getting our
USNR necks chopped off by putting our plan before
the President. Evening meetings were held with some of
his bright young men, who became most enthusiastic,
and arrangements were set for a presentation upon the
return of the President from his 194S spring vacation.
But, tragically, FDR died while still in Georgia on
April 12, 194S.

The expected change in the Navy Department then
happened, and on May 19, 1945, the Office of the Co-
ordinator of Research and Development was swallowed
up by the Office of Research and Inventions (ORI).
Also the Naval Research Laboratory and the Special
Devices Division of the Bureau of Aeronautics were
also transferred to ORI. Adm. Furer was out and Ad-
mirals Harold G. Bowen and Luis de Florez took over
with a bang. At the very outset it was a dreary time
for Capt. Conrad and the “bird dogs” as we feared our
dreams for the future would go down the drain. But
we had miscalculated. In a very short while Admirals
Bowen and de Florez took up the cudgels for an Of-
fice of Naval Research with great vigor. They solicited
the powerful backing of men like Commodore Lewis
Strauss, Under Secretary of the Navy W. John Ken-
ney, and Assistant Secretary H. Struve Hensel. In June
1945 Dr. Bush’s report to President Truman, entitled
Science, the Endless Frontier, appeared and had great
impact in Congressional and military circles. By Sep-
tember 1945 the “bird dogs” had a Congressional bill
all drafted for the establishment of an Office of Naval
Research to be headed, in deference to Mr. Forrestal,
by a Rear Admiral. This draft, which included the es-
tablishment of a Naval Research Advisory Committee
composed of eminent scientists, was to become known
as the Vinson Bill.

There remained one serious hurdle, outside of Con-
gressional action, before the establishment of ONR
could become meaningful. This was to get the Uni-
versities, where the majority of basic research is per-
formed, to be willing to accept Navy contracts. In this
struggle Capt. Conrad became the recognized leader.
Accompanied by various “bird dogs” Conrad visited
many top universities in the winter of 1945. There was
a definite feeling on the part of the scientists after four
years of war to wish to forget the Navy and return to
former pursuits. But Conrad was able to crumble all
opposition by making superb speeches around the coun-
try, and by working with legal and contract people to
pioneer an acceptable contract system. This would per-
mit one over-all contract with a university with new

task orders to be attached as agreed upon, permit basic
research to be contracted for, and permit the work to
be unclassified and publishable. Once the legal eagles
got this worked out, there was no holding the persuasive
Conrad, and he was quickly able to get such institu-
tions as Harvard, Chicago, University of California, Cali-
fornia Institute of Technology, and MIT to agree to
accept Navy work. Tragically, he contracted a lingering
but fatal case of leukemia at his moment of triumph.

With Adm. Bowen and his influential partners and
Capt. Conrad maneuvering effectively, the Vinson Bill
passed with flying colors and became Public Law 588
on August 1, 1946. It turned out to agree almost ver-
batim with the 1945 draft by the “bird dogs”. This
was indeed a day of rejoicing, culminating some four
years of effort entailing long hours of teaching, lots of
perseverance, and even a little intrigue. As stated at the
outset, the victory belonged not to a few, but to many
scientists, naval officers, and political figures, some of
whom are still unrecognized.

Unexpected Contribution

* I ''HE impact of this victory was destined to go far

A beyond the expectations of the authors. By dint of
this far-sighted planning, coupled with favorable action
by Congress, the Navy found itself the sole government
agency with the power to move into the void created
by the phasing out of the OSRD at the end of the War.
While Congress still debated what to do about a na-
tional agency, Forrestal, Bowen, now Chief of Naval
Research, and de Florez arranged for war-end money
transfers, and ONR moved forward aggressively to
bridge the gap. Sound policies set by the Naval Re-
search Advisory Committee were admirably carried out
under the guidance of Capt. Conrad and Dr. Alan
Waterman. The world leadership of the United States
in basic research in the decade following World War II
has been largely credited by many experts to the timely
and effective work of the Office of Naval Research.

Surprise Ending

TT was previously stated that the “bird dogs” sug-
gested and worked for, even at some risk, the ap-
pointment of an Assistant Secretary of the Navy for
Research as representing the ideal organizational solu-
tion to assure research the representation and emphasis
it deserves in the development of a Navy second to
none in this age of science. Continued education and
pressure by many people finally brought about such a
move in 1959. Perhaps it was a case of poetic justice,
but, at any rate, the rest of the “bird dogs” are happy
and proud to report that the very first man appointed
to the office of Assistant Secretary of the Navy for Re-
search was one of us.

If the recording of this brief history will but inspire
continued constructive efforts by other lowly “bird
dogs” in government, we will feel more than amply re-
warded.

101

^—Chapter 3 -
Social Context

Like any human enterprise, physics is inextricably
entangled in its social context, that is, in history at
large. Articles in the previous section showed the internal
workings of single, specific institutions; here we look at the
whole community of physicists — as an entity of itself and as
something profoundly affected by the rest of society. (Of
course the physics community has had in return a
tremendous impact on society, but that is another story.)

Surprisingly often, the history of social relations gets
into topics that are of lively current interest. The physics
community painted by Nagaoka’s letters to Rutherford was
a hundredth the size of our current enterprise, but the
standard of courtesy and the method of learning by
traveling remain valid whenever relations between
"developed” and "developing” countries are as open as
they were between Europe and Japan in 1911. Physics
education in general, especially in its relations with
engineering, is still more a topic where a look at history
may help to save people from repeating, as if they were
invented yesterday, arguments that have in fact been
worked over vigorously for many decades. On the other

hand, discrimination against women and certain other
groups as scientists, although it is one of our oldest
problems, was discussed all too little until recent years —
the article in this section is the only extended historical
treatment we have seen in any journal read by physicists.

Other issues of social relations have taken on grave
significance only recently. "Recently” to historians means
within the past few decades; there has been enough time to
accumulate some experience. As the articles here suggest,
the impact of economics on physics in the 1930s was
repeated in some respects in the 1970s. As for questions of
secrecy, and more generally of the role the federal
government should play in science, questions which first
became urgent around the time of the Second World War,
these are still more urgent today. More generally still, the
unprecedented and revolutionary reorganization of
physics as a whole, both internally and in its relations to
society, which took place within the past fifty years, is
something that we can only come to grips with if we
understand just what has changed and what has not.

Contents

103 Nagaoka to Rutherford, 22 February 1911 Lawrence Badash

108 American physics and the origins of electrical engineering Robert Rosenberg

115 Physics in the Great Depression Charles Weiner

123 Scientists with a secret Spencer R. Weart

130 Some thoughts on science in the Federal government Edward U. Condon

138 Fifty years of physics education A. P. French

149 Women in physics: unnecessary, injurious and out of place? Vera Kistiakowsky

159 The last fifty years — A revolution? Spencer R. Weart

I

i

a.

SOCIAL CONTEXT

103

Nagaoka to Rutherford,
22 February 1911

During 1910, the physicist Hantaro Nagaoka represented
Japan at two international scientific congresses in Brussels
and one in Vienna. This visit to Europe gave him an oppor-
tunity to observe the latest researches in the various centers
of physics and to renew many acquaintances from his student
days in Germany. He called at Manchester before continuing
to the continent, and the letter he later wrote to Rutherford
is both a description of the state of physics through the eyes
of an acute observer and a “ thank you” to Rutherford.

PHYSICS TODAY / APRIL 1967

btj Lawrence Badash

What was physics like slightly more
than half a century ago? One readily
thinks of such famous names as J. J.
Thomson, Ernest Rutherford, Marie
Curie, Max Planck, Niels Bohr, H. A.
Lorentz, Albert Einstein, et al, but
these are the highlights of hindsight.
For the background of perhaps lesser,
but nevertheless significant and inter-
esting efforts, we usually must look to
the contemporary literature, since his-
tories of science rarely have room for
elaborate descriptions of a period.

The letter printed below contains
the impressions of an eminent physi-
cist who visited a good many physical
laboratories in Europe during the last
quarter of 1910. Years earlier, its au-
thor, Hantaro Nagaoka (1865-1950),
had studied in Berlin, Munich, and
Vienna, and was, therefore, renewing
old acquaintances as well as familiariz-
ing himself with the latest continental
research activities. Since 1906, he had
been professor of theoretical physics
at the Imperial University of Tokyo;
and many years later he was to become
the president of the Imperial Univer-
sity of Osaka.

The recipient of this letter, Ernest
Rutherford (1871-1937), needs no

identification in physics today, other
than to indicate that at this time he
was professor of physics at the Univer-
sity of Manchester. Nagaoka had vis-
ited Rutherford’s laboratory in Sep-
tember 1910, and now, happily,
thought to describe his trip in this let-
ter of thanks for his host’s hospitality.

Still classical physics

In this letter it is interesting to note
the widespread activity in “classical”
physics, which had by no means en-
tirely been superseded by the increas-
ing amount of research in “modern”
physics. This is a point we too often
overlook. One final note of interest is
that, coincidentally, Nagaoka’s best
known scientific contribution derives
its fame from the work of Rutherford.
When the latter published his concept
of the nuclear atom in 1911, it was
seen that Nagaoka’s “Saturnian” atom
of 1903-1904 was something of a pre-
cursor. Though there was no direct
influence of this earlier work upon
Rutherford, and in fact their atoms
bear many dissimilarities, these con-
structs of Nagaoka and Rutherford
frequently have been associated in
popular literature. It is not impossi-

ble, however, that the two discussed
the Saturnian atom in September 1910
and that the concept remained subcon-
sciously in Rutherford’s mind, bearing
fruit in the next year.

February 22nd, 1911
Physical Institute,
Tokyo University

Dear Professor Rutherford,

I have completed my “Studienreise”
in Europe and returned home a few
weeks ago, and have the pleasure of
writing you some of my impressions
during the journey. In the first place,
I have to thank you for the great kind-
ness, which you have shown me dur-
ing my visit to Manchester. I have
been struck with the simpleness of the

Lawrence Badash
teaches history of
science at the Uni-
versity of California,
Santa Barbara. He
did this work in
Cambridge, England,
supported by a
NATO fellowship
and an NSF grant.

104

HISTORY OF PHYSICS

apparatus you employ and the brilliant
results you obtain. Everybody en-
gaged with the investigations on radio-
activity seems to be impressed with
the same fact and expresses admira-
tion of the splendid results, which you
obtain with extremely simple means.

Lowest temperature yet

The “Kaltekongress” in Vienna was
too technical for me; it was in fact a
congress for the industry of refrigera-
tion. The only scientific paper of im-
portance was a report by Kamerlingh-
Onnes on the lowest temperature hith-
erto attained. By boiling liquid heli-
um in vacuum, he claims to have
reached the temperature of 2.5° from
absolute zero. Later on I visited his

laboratory in Leyden and saw his cas-
cade process of reducing the tempera-
ture. He tells me that the greatest
difficulty lies in the purification of
gases; a millionth part of hydrogen
mixed with helium would deteriorate
the process of liquefaction. It will be
quite interesting to experiment on the
radioactivity at the temperature of
—270°, if such cold can be maintained
for a sufficient length of time. I met
Planck in Berlin and asked his opinion
as to the change which would be
wrought on radioactivity. His con-
jecture on the change of A in the
neighborhood of absolute zero is in
the affirmative, based on several con-
siderations depending on the theory
of radiation.

At the time I visited Vienna, the
radium institute was not yet complete-
ly built, but I met St. [efan] Meyer in
the old laboratory of Boltzmann and
Exner. In Graz, I was happy to see
my old friend Benndorf, who studied
with me in Berlin and Vienna about 16
years ago. He was occupied with the
registration of the atmospheric elec-
tricity and seemed much interested in
seismology, which has special charm
for Japanese on account of the vol-
canic character of the Japanese is-
lands. It was very curious that most
of my opinions respecting earthquakes
were in accord with those of Benndorf,
although I am quite at variance from
Japanese seismologists.

Righi in Bologna was much interest-

Cast of Characters — People Mentioned by Nagaoka

Hans Benndorf (1870-1953). Phys-
ics professor, University of Graz,
after 1910.

Ludwig Boltzmann (1844-1904).
Physics professor, University of Vi-
enna, from 1902 to 1906. Earlier
at Munich. Famous for his part in
the introduction of statistical me-
chanics.

Alfred Bucherer (1863-1927). Pri-
vatdozent, University of Bonn, after
1899; later professor.

Peter Debye (1884-1966). Privat-
dozent, University of Munich,
1910-1911. Later professorial posi-
tions at Zuerich, Utrecht, Goettingen,
Berlin and Cornell. Nobel Prize in
chemistry in 1936 for his studies of
molecular structure.

Hermann Ebert (1861-1913). Mathe-
matics professor, Technische Hoch-
schule, Munich, after 1898.

Felix Ehrenhaft (1879-1952). Assist-
ant in Physical Institute, University
of Vienna, 1904-1910; professor
after 1911.

Franz Exner (1849-1926). Physics
professor, University of Vienna, after
1891. Interested in spectroscopy,
particularly the lines of the ultravi-
olet region.

Carl Friedrich Gauss (1777-1855).
The “Prince of Mathematicians” was
mathematics professor and director
of the Goettingen astronomical ob-
servatory, after 1807. Concerned
also with terrestrial magnetism.

Ernst Gehrcke (1878-1960). Physi-
cist at the Physikalische-Technische
Reichsanstalt, Berlin; later director.

Charles Guye (1866-1942). Physics

professor, University of Geneva,
after 1900.

Friedrich Harms (1876-1946). As-
sistant in the Physical Institute, Uni-
versity of Wuerzburg, after 1901;
later professor.

Johannes Hartmann (1865-1936).
Astronomy professor, University of
Gottingen, after 1909. Spectroscop-
ist interested in continuous spectra
due to atoms.

Hermann von Helmholtz (1821-
1894). Physics professor, Uni-
versity of Berlin, 1871-1894; presi-
dent of the Physikalische-Technische
Reichsanstalt, Charlottenburg,
1888-1894; Famous for his work in
physiology, sound and conservation
of energy.

Heinrich Hertz (1857-1894). Phys-
ics professor, University of Bonn,
from 1889 to 1894. Famous for his
discovery of the electromagnetic
waves predicted by Maxwell.

Ludwig Janicki (1879-????). Physi-
cist at the Physikalische-Technische
Reichsanstalt, Charlottenburg.

Heike Kamerlingh-Onnes (1853-
1926). Physics professor, Univer-
sity of Leiden, after 1882. Nobel
Prize in 1913 for low-temperature in-
vestigations.

Heinrich Kayser (1853-1940).
Physics professor, University of
Bonn, after 1894. With C. Runge,
he determined that the distribution
of spectral lines has a regularity.
Suekichi Kinoshita (1877-1933).
Physics instructor, University of
Tokyo, after 1909. Later professor.
Peter Paul Koch (1879-1945). Pri-
vatdozent, University of Hamburg;
later professor.

Friedrich Kohlrausch (1840-1910).
Physics professor, University of
Wuerzburg, from 1875 to 1888; Uni-
versity of Strassburg, 1888 to 1895;
then president of the Physikalische-
Technische Reichsanstalt, Charlot-
tenburg, 1895 to 1905. Explained
electrolytic conductivity by dissocia-
tion hypothesis.

August Kundt (1838-1894). Phys-
ics professor, University of Berlin,
from 1888 to 1894. Studied anom-
alous dispersion in liquids, vapors
and solids; devised method of com-
paring sound velocities in gases and
in solids.

Otto Lehmann (1855-1922). Phys-
ics professor, Technische Hoch-
schule, Karlsruhe, after 1889. Dis-
covered the unexpected existence of
crystalline arrangement in some
liquids.

Philipp Lenard (1862-1947). Phys-
ics professor, University of Heidel-
berg, after 1907. Nobel Prize in
1905 for his work on cathode rays.
Hendrik Antoon Lorentz (1853-
1928). Physics professor, Univer-
sity of Leiden, after 1878. Shared
1902 Nobel Prize with Zeeman for
his study of the influence of magne-
tism on radiation.

Otto Lummer (1860-1925). Physics
professor, University of Breslau,
after 1905. Noted for his experi-
mental study of black-body radia-
tion.

Stefan Meyer (1872-1949). Physics
professor, University of Vienna, after
1908. In charge of the Radium In-
stitute, and a leader in the field of
radioactivity.

Alexander Pflueger (1869-1945).

SOCIAL CONTEXT

105

ed with my model of Saturnian atom
published in 1904. He showed me his
different apparatus on electric waves
and the so-called magnetic rays. O.
Lehmann in Karlsruhe seems to have
made similar experiment with a colos-
sal tube of several meter length and
arrived at results similar to Righi. In
Geneve, I met Guye and Sarasin. The
latter gentleman has been kind enough
to show me all the notorieties and fine
sceneries of Geneve. He told me of
your visit there and how you laughed
“von ganzem Herzen,” if I may be
permitted to use Sarasin’s language.

80 000-gauss magnets

The speciality of the physical insti-
tute in Zurich seems to be electromag-

nets. Weiss showed me one of 1000
Kilogrm. weight, with which he can
get a field strength of 80 000 gauss in
space of 2 mm., a somewhat extraordi-
nary figure.

In Munich, I saw Ebert’s apparatus
for registering the quantity of emana-
tion coming out of the soil. What
seemed to me new and interesting was
the section for technical physics.
There are various investigations going
on in connection with the applications
of physics to technical purposes. Un-
fortunately I could not see Rontgen, as
he was away from the city. Koch tells
me that he could measure Zeeman ef-
fect in field of 3 gauss by photograph-
ing the lines and comparing the in-
tensity by means of Hartmann’s pho-

Physics professor, University of
Bonn, after 1905.

Max Planck (1858-1947). Physics
professor, University of Berlin, after
1892. Nobel Prize in 1918 for dis-
covery of energy quanta.

Erich Regener (1881-1955). Phys-
ics professor, agricultural Hoch-
schule, Berlin, after 1914; later at
Technische Hochschule, Stuttgart.
Noted for method of counting alpha
particles by scintillations.

Augusto Righi (1850-1920). Phys-
ics professor, University of Bologna,
after 1889. Improved Hertz’s vibra-
tor, or wave-radiating apparatus.
Wilhelm C. Roentgen (1845-1923).
Physics professor, University of
Munich, after 1900. Nobel Prize in
1901, the first year it was awarded,
for his discovery of x rays, made at
the University of Wuerzburg.

Heinrich Rubens (1865-1922).
Physics professor, University of Ber-
lin, after 1906. Studied black-body
radiation.

Jean Edouard Charles Sarasin (1870-
1 933). Geology and paleontology profes-
sor, University of Geneva, after 1 896.

Clemens Schaefer (1878-????).
Physics professor, University of Bre-
slau, after 1910.

Arthur Schuster (1851-1934).
Physics professor, University of
Manchester, from 1881 until he re-
tired in 1907 to allow Rutherford to
succeed him.

Arnold Sommerfeld (1868-1951).
Physics professor, University of
Munich, after 1906. Noted for his
refinement of Bohr's original atom

picture, by the introduction of orbi-
tal quantum numbers.

Johannes Stark (1874-1957). Phys-
ics professor, Technische Hoch-
schule, Aachen, after 1909. Nobel
Prize in 1919 for his discovery of the
Doppler effect in canal rays and the
splitting of spectral lines in electric
fields.

Emil Take (1879-1925). Privatdoz-
ent, University of Marburg, after
1911; later professor.

Woldemar Voigt (1850-1919).
Physics professor, University of
Goettingen, after 1883. Explained
Kerr effect using electron theory.
Wilhelm Weber (1804-1891). Phys-
ics professor, University of Goettin-
gen, after 1849. Associated with
Gauss in terrestrial magnetism, tele-
graphy, mathematical physics. In-
troduced absolute units in electric-
ity.

Pierre Weiss (1865-1940). Physics
professor, Polytechnicum, Zuerich,
after 1903. Introduced the word
"magneton” to represent an elemen-
tary magnet, in a theory of magne-
tism.

Johann Emil Wiechert (1861-1928).
Geophysics professor, University of
Goettingen, after 1898.

Wilhelm Wien (1864-1928). Phys-
ics professor, University of Wuerz-
burg, after 1900. Nobel Prize in
1911 for his study of black-body ra-
diation.

Pieter Zeeman (1865-1943). Phys-
ics professor, University of Amster-
dam, after 1900. Nobel Prize in
1902, shared with Lorentz, for dis-
covery of magnetic broadening of
spectral lines: Zeeman effect.

NAGAOKA

RUTHERFORD

DEBYE

106

HISTORY OF PHYSICS

tometer. When I studied in Munich
in 1894 under Boltzmann, the institute
was very poor, but it is now rebuilt
and there is also an institute for
theoretical physics under Sommerfeld,
who is working on the principle of rel-
ativity, and Debye expounded mathe-
matical formulae for the pressure of
light acting on a dielectric or metallic
sphere.

In Amsterdam I saw Zeeman in-
vestigating the effect bearing his
name in various lines of research. In
Leyden, Lorentz was discussing Eh-
renhaft’s curious result on the charge
of electrons, but afterwards I learned
in Berlin that the experiment was en-
tirely wrong. Stark in Aix-la-Chapelle
[Aachen] was propounding his “Licht-
quantentheorie”; there is some doubt
whether he will succeed in explaining
the interference phenomena, or not.
The Germans say that he is full of
phantasies, which may be partly true.
In Bonn I failed to see Bucherer, but
his experiment on e/m is now re-
peated by C. Schafer in Breslau, and
I hope we shall be able to hear his re-
sult in the near future. Kayser’s spec-
troscopic researches are worth seeing;
instead of moving the grating and
keeping the slit fixed, he uses the re-
versed method of turning the slit on a
fixed circle while the grating is fixed
on a stout pier. This will be some-
times advantageous in photographing
the spectrum. Pfliiger, with whom I
worked in Kundt’s laboratory in 1893,
showed me a number of interesting
apparatus. He has pasted thin quartz
plates on a rocksalt prism and investi-
gated the infrared as well as the ultra-
violet rays with as much success as
with fluorite or quartz prisms. A
vacuum tube used by Hertz to demon-
strate the passage of cathode rays
through thin aluminum plate is one of
the historical treasures of the physical
institute of Bonn.

Discharges and x rays

The radiological institute in Heidel-
berg under Lenard is perhaps one of
the most active in Germany. Professor
Lenard and most of his pupils are
working on the phosphorescence and
photoelectric action. In Wurzburg, I
saw the room where X ray was discov-
ered by Rontgen. Various researches
on canal rays are going on under the
direction of W. Wien. The famous

WIEN

SOMMERFELD

LORENTZ

ROENTGEN

LENARD

STARK

SOCIAL CONTEXT

107

magnetic observatory without iron,
built by Kohlrausch, is now rotten;
more important works on vacuum dis-
charge have absorbed the attention of
Wurzburg physicists. In the collo-
quium, Harms gave a report of your
paper on the calculation of a particles,
which was in progress when I visited
Manchester. All the members present
expressed great admiration at the
splendid result obtained with such a
simple device. It seems to me that it
is only a genius, who can work with
simple apparatus and glean rich har-
vest far surpassing that attained with
the most delicate and complex ar-
rangements.

[In his reply to Nagaoka, 20 March
1911, Rutherford noted: “I very much
appreciate your kind references to
myself and to my work. I did not
know that the simplicity of my experi-
ments was so unusual. As a matter of
fact I have always been a strong be-
liever in attacking scientific problems
in the simplest possible way, for I
think that a large amount of time is
wasted in building up complicated
apparatus when a little forethought
might have saved much time and
much expense.”]

Liquid crystals

In Karlsruhe, the original apparatus
of Hertz for demonstrating electro-
magnetic waves were most attracting.
They are as simple as are most of your
apparatus. Lehmann is busily occu-
pied with the investigation of the so-
called liquid crystals. The appearance
of several substances in polarised light
is quite phantastic and accords with
the illustrations given by him. The
only point of doubt is that these crys-
tals appear only in the neighbourhood
of the melting point, and may be
closely connected with the changes in
the aggregate condition. It is quite
certain that in the present stage differ-
ent views are entertained as to the na-
ture of the liquid crystals.

Strassburg was interesting to me as
a centre of seismological association;
great changes are going on in the staff
of the central bureau, and it is to be
congratulated for the science of
seismology that the reorganisation will
produce good effect on the interna-
tional investigation of earthquakes.
We have to thank Prof. Schuster for
the lively interest he takes for the as-

sociation, and the great effort he has
made to strengthen the weak associa-
tion, by recruiting it with personages,
who can investigate earthquakes phys-
ically [better] than it has hitherto been
examined statistically and with defec-
tive instruments.

Frankfurt, Leipzig, Breslau
Frankfurt has built a fine physical
institute with rich equipments. It is
curious that the city well known for its
immense wealth has not yet estab-
lished a university within its precinct.
The magnetic properties of Heusler
alloy is now being investigated by
Take in Marburg; the artificial means
of aging the alloy seems to effect inter-
esting magnetic changes. Voigt’s lab-
oratory in Gottingen is justly cele-
brated for the numerous works, which
are connected with the physics of crys-
tals and the magneto- and electro-op-
tics. There were more than 20 re-
search students. The famous mag-
netic observatory of Gauss and Weber
is now removed to the environs of
Gottingen. Wiechert has installed an
extremely sensitive seismometer, which
records vibrations due to storm in the
North Sea. He showed me traces of
shocks due to dynamo engine in Got-
tingen.

The physical institute in Leipzig is
perhaps the largest in Germany; but I
find that the largest is not always the
best. However poor the laboratory
may be, it will flourish if it has earnest
investigators and an able director.
The size and the equipment of the lab-
oratory seems to me to play a second-
ary part in the scientific investigations.
The splendid institute in Breslau has
been newly built by Lummer. The in-
vestigations are mostly optical; the
different kinds of interferometers and
the photometers are the essential
equipments of the institute. Besides
Lummer, C. Schafer is working in
electric waves and applications of in-
tegral equations to different problems
of theoretical physics.

The works going on in the Physikal-
ische Reichsanstalt in Berlin is some-
what akin to those in the National
Physical Laboratory. Some measure-
ments are nervously delicate that we
can not help crying out qui bono. The
[illegible] -rohr and Glimmlichtrohr of
Gehrcke are very interesting, and the
inventor claims to use the latter tube

as an oscillograph for high frequency
up to 100,000 cycles per second. The
investigations of spectral lines by Jan-
icki will form a good contribution to
our knowledge on the nature of atomic
vibrations.

In the physical institute of Berlin, I
saw Rubens who showed me his ar-
rangement of “Reststrahlen” for isolat-
ing light waves of 96 jj„ Regener was
repeating Ehrenhaft’s experiment and
announced that the result was entirely
wrong, so that there can not exist a
charge, which is a fraction of that of
an electron. While visiting the insti-
tute, I chanced to enter the rooms
where I heard the lectures by
Helmholtz and where I worked under
Kundt in 1893. They made me deeply
impressed how swiftly time is gliding;
and while thus writing it reminds me
that 5 months has passed away since I
saw you in Manchester.

Cold in Siberia

I returned by way of Siberia and ex-
perienced the low temperature of
— 44 °C on the Chinese frontier. The
car was comfortable, but the tempera-
ture difference of 60° in and out of the
car was almost unbearable. The con-
sequence was that I caught a severe
cold and was confined to bed for about
three weeks. I have as yet nothing to
write you about the scientific investi-
gations in Japan. Kinoshita is going to
start radioactive works with the
radium, which you have kindly pro-
cured for him.

Please remember me to Mrs. Ruth-
erford and your daughter.

Wishing you much scientific suc-
cess,

I remain

Yours faithfully
H. Nagaoka

* * *

For access to this letter and permission to
print it and for permission to quote
Rutherford’s reply, I am indebted to: the
family of Professor Nagaoka, Mr. T.
Kimura and Dr. E. Yagi of the Commit-
tee for the Publication of Nagaoka’s
Biography, the grandchildren of Lord
Rutherford, the authorities of the Caven-
dish Laboratory, and the Cambridge
University Library. Nagaoka’s letter is
preserved at the Cambridge University
Library; Rutherford’s reply is in the
possession of the Committee for the Pub-
lication of Nagaoka’s biography. A few
spelling errors in Nagaoka’s 14-page long-
hand original have been corrected in the
editing. □

1

108

HISTORY OF PHYSICS

American physics
and Hie nrigins nf
electrical engineering

Pure physics applied: academic physics gave birth

to a new practical discipline with its

own priorities and its own departmental structure.

Robert Rosenberg

At the same time that electricity was
transforming American society in the
last half of the 19th century, it was
transforming the study of physics.
During this period, electricity bridged
the existing gap between pure science
and useful applications, between think-
ers and doers, scholars and tinkers, as
no other technology had done before. It
brought home to Americans the contri-
butions of science to everyday life. It
also quickened the pace of physics
research in university classrooms and
industrial laboratories.

Together, electricity and physics held
immense promise for the future — a pro-
mise unnoticed at the Philadelphia cen-
tennial exhibition of 1876, with its small
displays of telephones and dynamos, but
visible to all at the opening in 1883 of the
Brooklyn Bridge, illuminated by Edward
Weston’s arc lights. It happens that both
dates are reference points for US physics.
In 1876, Henry Augustus Rowland, edu-
cated as an engineer but dedicated to ba-
sic research, became the first professor of
physics at the newly founded Johns Hop-
kins University in Baltimore, and, in
1883, Rowland proclaimed in his vice-
presidential address to the American As-
sociation for the Advancement of Science
that henceforth the word “science”
should no longer be applied to the tele-
graph, telephone, electric light or electric
motor. With the advent of electrical tech-

Robert Rosenberg, a doctoral candidate in the
History of Science Program at The Johns
Hopkins University, has been recently ap-
pointed a research associate on the Edison
papers project at Rutgers University.

PHYSICS TODAY / OCTOBER 1983

nology, American physicists could choose
to be theoretical or practical — or both.

The connection and then disconnec-
tion of basic physics and electrical
engineering had been made years ear-
lier in Europe. In Britain, such theo-
rists as James Clerk Maxwell and John
William Strutt (Lord Rayleigh) at Cam-
bridge University had a great impact
on technology, but their immediate
influence was indirect since few engi-
neers could understand them. It took a
creative effort almost equal to that of
Maxwell and Rayleigh by Oliver Heavi-
side, a British engineer with no formal
education past the elementary level, to
translate their electromagnetic equa-
tions into a usable form, and even
Heaviside’s work was unintelligible to
most engineers. Yet Maxwell and Ray-
leigh were among those physicists who
consciously attempted to contribute to
technology. Others include Heaviside’s
uncle, Sir Charles Wheatstone of
King’s College, London, who somewhat
anticipated Samuel F. B. Morse in
developing the telegraph, and William
Thomson (Lord Kelvin) at Glasgow,
who virtually single-handedly engin-
eered the cables, galvanometers, and
other electrical components for the
first successful telegraph cable beneath
the Atlantic Ocean in 1866.

By the 1880s, the need for rigorous
training in electrical engineering was
becoming clear to many. Werner Sie-
mens, Germany’s leading industrialist
of the period, urged his country’s tech-
nical schools to introduce courses in
electrical engineering and, with a lead-
ing physicist, Hermann von Helmholtz,
he persuaded the government to estab-
lish a national laboratory in 1882.
Around that time, William Ayrton

attempted to organize in London the
sort of laboratory instruction in elec-
tricity that he and John Perry had
carried on in the late 1870s at Japan’s
Imperial College of Engineering.

Electrical innovations

Such examples did not go unnoticed
in the US, though the order of events
was somewhat different. By the late
1870s, the considerable body of know-
ledge produced by rapidly advancing
research on electricity in Europe had
crossed the Atlantic, and by the end of
the century electric innovations in the
US had provided an ineluctable justifi-
cation for supporting physics teaching
at universities and research work in
companies. In the US it was not the
physicist — such as J. Willard Gibbs at
Yale or Henry Rowland at Johns Hop-
kins— who caught the public imagina-
tion, but the inventor — Edison, Charles
Steinmetz, Nikola Tesla — working in
commercial surroundings.

The success of electrical technology

SOCIAL CONTEXT

109

had two effects on American physics.
First, students eager to understand the
new electrical technology and to contri-
bute to it, as well as to profit from it,
put an unceasing strain on the budgets
and facilities of physics departments in
universities, colleges, and technical
schools. Of some 400 colleges and
universities surveyed by T. C. Menden-
hall for the US Bureau of Education in
1882, almost all offered some instruc-
tion in physics, but only 20 had even
minimal laboratory facilities. In the
many large physical laboratories built
during the 1880s, the lion’s share of
space was devoted to the study of
electricity and magnetism.

Second, the social impact of electrical
technology confirmed the claim of phy-
sicists that their investigations led to
material progress. In 19th-century
America, this was an important point.
Chemistry had already demonstrated
its utility in agriculture and industry,
and biology was linked with medicine,
but until the growth of electrical tech-

nologies, physics held little claim to
being utilitarian. The source of the
new technologies was in research, both
pure and not so pure.

Dynamo as symbol

As long as it emphasized power and
light, electrical engineering needed a
solid foundation of physics and me-
chanical engineering. It is somewhat
surprising, then, that early electrical
engineering education was under the
direction of physics teachers. Mechani-
cal engineers did not involve them-
selves because in the early 1880s me-
chanical engineers did not understand
electricity. Thus, although a paper
presented in 1882 to the American
Society of Mechanical Engineers on the
Edison Steam Dynamo — the combina-
tion steam engine and dynamo that
was to power the Pearl Street Station
in New York City — treated both compo-
nents of the machine, the lengthy
discussion that followed was entirely
about the steam engine. One promi-

Electrical engineering students at Cornell’s
Sibley School in the 1890s learning about
the design of street railway motors. Subject
of study is written on blackboard at rear of
class. (Courtesy Cornell University Archives.)

nent engineer, puzzled by the working
of the dynamo, said, “There may be
electrical reasons for this construc-
tion.” What those reasons were, he had
no idea.

Mechanical engineers recognized
(and laughed about) the mechanical
ignorance of many electrical engineers,
and sometimes referred to Sir William
Thomson’s dictum that an electrical
engineer should be 90% mechanical
and 10% electrical. Until the end of
the 1880s, however, when electric mo-
tors began to compete successfully with
steam as a power source, mechanical
engineering as a profession had little to
do with electricity. By the time the
mechanical engineers became con-
cerned about the encroachment of elec-
tric power, the electrical engineers had
their own discipline, their own profes-
sional image, and their own ideas about
how to educate students.

In the early 1880s, the need for
formal education in electrical engineer-
ing was becoming manifest. The editor
of The Electrician, a New York trade
journal, wrote in April 1882:

There is now a rapidly growing
want for men trained in the theory
and practice of the science of elec-
tricity. . . . The demand is estab-
lished, and it now behooves our
foremost educators to devise a
means of satisfying it.

An American just back from Europe
wrote a letter to the student paper at
Cornell in September 1882, urging
undergraduates to consider the new
profession of electrical engineer now
being taught abroad.

The enormous extension of the
telegraph, telephone, electric light,
etc., into all parts of the world will
create a great demand for skilled
electricians at no very distant day.
To which the editors added,

We wish to recommend this spe-
cially to the students of Cornell
University as a department well
worthy of their careful investiga-
tion.

That fall, Edison wrote to the presi-
dent of Columbia College suggesting
that a course in electrical engineering
should be given in the School of Mines
and offering his electrical collection to
the College as a museum.1 Although
Edison often publicly belittled academ-
ics and universities, he employed physi-
cists, chemists and metallurgists and

110

HISTORY OF PHYSICS

even consulted with college professors
and read scientific journals. During
the 1880s he contributed many thou-
sands of dollars in equipment for elec-
trical engineering programs at several
schools. Columbia did not establish a
course in electrical engineering until
the end of the decade, by which time
most universities were already actively
teaching electrical science in their
physics departments.

First course in EE

The first formally structured course
in electrical engineering appeared in
1882. But the roots of that course were
embedded in the 1870s, when such
academic physicists as Charles Cross at
MIT and William Anthony at Cornell
began to shape their teaching around
the new discoveries in electricity.

In 1869, Edward C. Pickering, profes-
sor of physics at MIT, established the
first systematic laboratory instruction

in physics in the country.2 In the 17
classes preceding the initiation of the
electrical engineering course at MIT,
only six of the 361 graduates took
degrees in physics. The reason for the
lack of interest in a physics degree is
not hard to ascertain. It could be found
in MIT’s 1881-1882 catalog (and had
been noted by Rowland at Johns Hop-
kins four years earlier): “Most of the
students taking the course in Physics
intend to make teaching their profes-
sion.” Unfortunately, there were few
openings for physics teachers in the
1870s and early 1880s.

Cross had graduated from MIT in
1870, one of a class of ten, the only
student in the General Science and
Literature course. He at once became
an instructor in the physics depart-
ment, a professor in 1874, and head of
the department on Pickering’s depar-
ture in 1877. Cross had an intense
interest in electricity. In his 1873

report to the president of the Institute,
he noted:

The most defective portion of the
apparatus designed for lecture-
room use is that relating to elec-
tricity and magnetism, upon which
a considerable sum must be spent
in order to make it a fair represen-
tation of the present state of elec-
trical science.

The next year some electrical appara-
tus, including an induction coil, was
obtained by the department, and the
electrical inventor Moses Farmer
loaned the Institute one of his magneto-
electric machines. In 1876, six electri-
cal experiments were offered in the
laboratory. The same year, Cross hired
Silas Holman of the class of 1876 (in
physics) as a laboratory assistant. Hol-
man was an important part of the
physics department for more than 20
years, contributing greatly to the elec-
trical engineering program.

By the spring of 1878, electrical
questions were appearing on examina-
tions for second-year students of phys-
ics. Examples:

What is a Thomson’s galvanom-
eter and what advantages has it
over the ordinary form?

What is a commutator?

What is a shunt, and when used?
The next year, the first-term examina-
tion for the juniors had a question on
Ohm’s law. Four of seven questions on
the same examination one year later
(in January 1880) dealt with electrical
subjects — the theory of the voltaic cell,
Lenz’s law, Ohm’s law, and the oper-
ation of induction coils, telegraphy and
dynamos.

In 1881, the MIT catalog announced:

On alternate years a course of
lectures will be given upon the
scientific principles involved in the
more recent applications of Elec-
tricity including the Telegraph,
the Telephone, Electric Lighting,
and the transmission of power by
electricity.

The next year, with the addition of “an
extended course of Laboratory instruc-
tion in electrical measurements,” the
lecture course became the senior-year
instruction in the new “alternative
course in Physics ... for the benefit of
students wishing to enter upon any of
the branches of Electrical Engineer-
ing.” Two years later the course would
be formally called Electrical Engineer-
ing, but with no significant change in
content. In fact, the establishment of
the “alternative course in Physics” in
1882 involved little more than the
shuffling of existing courses to effect a
marriage of physics and mechanical

Henry Rowland of Johns Hopkins, one of
the leading US physicists, in a portrait by one
of the nation’s greatest artists of the period,
Thomas Eakins.

I

SOCIAL CONTEXT

111

engineering. It was just the next step
in a natural evolution, rather than a
restructuring or redirecting of Cross’s
teaching.

At MIT, electrical engineering in-
struction kept the physics staff busy.
Electrical engineering students had as
much physics as the physics students
and then some. In the first year of the
course, 18 students were registered,
and in the second year, 30. In succes-
sive years, it continued to grow, and in
1889 was the best-attended program at
the Institute, with 105 students. More-
over, in 1891, some 23 students gradu-
ated in electrical engineering, while
only three took physics degrees. In
1896, electrical engineering degrees
were given to 48 students, while the
number receiving degrees in physics
was still three.

At Cornell, much the same evolution
was taking place. Anthony had come
to Cornell in 1872 with a high reputa-
tion in physics. When Anthony was
hired away from the Iowa Agricultural
College, Cornell’s vice-president Wil-
liam C. Russel told the university’s
president, Andrew D. White, that the
school had acquired a “tower of
strength.”3 Anthony was an exception-
al teacher and an adept experimental-
ist, and kept himself fully informed on
current developments in his science.
He possessed the idealism of a pure
scientist and the practical bent of an
engineer. The prospect of a position at
Cornell was enticing. He wrote to
Russel in 1872:

I judge that your standard of schol-
arship is higher [than at Iowa], and
that your aim is to make scholars,
as well as impart “practical” know-
ledge. I want to get into an atmo-
sphere where the grandeur and
beauty of scientific truth are recog-
nized and where science is valued
for itself.

In 1873, after enumerating for White
the many possible uses for physics in
the modern world, he added:5
But I should not consider the
teaching of the practical applica-
tion of physics to be the highest
purpose of the physical laboratory.

I should hope that young men
would be found who would wish to
pursue the science for its own sake.

I should wish to furnish to such an
opportunity to make investiga-
tions that would advance the inter-
ests of science.

To further this end, Anthony had made
his acceptance of the job conditional on
the university’s purchase of at least
$15 000 worth of apparatus in his first
five years there.6

Funding problems

Had Cornell not fallen on hard times
in the 1870s (as did MIT and many
other institutions), the physics depart-

Three illustrious
physicists of the late
19th century
(clockwise from top
left), William Anthony
of Cornell (photo
courtesy Cornell
University Archives),
his successor, Harris J.
Ryan (Cornell College
of Engineering), and
Edward Pickering of
MIT (with muttonchop
whiskers), who was
photographed here on
an outing with
academic colleagues
(Hale Observatory,
Courtesy AIP Niels
Bohr Library).

ment might have achieved prominence
earlier than it did. Certainly Anth-
ony’s career there would have been
quite different. As it was, in the spring
of 1873 Anthony had to give a course of
popular lectures during vacation to
raise money for apparatus, and when
he resigned 14 years later it was partly
out of frustration at being denied $1500
for instruments.

But although financial embarrass-
ment was a hindrance to Anthony’s
department, the development of elec-
trical science was tremendously stimu-
lating. Anthony’s interest in electri-
city was even more precocious than
Cross’s. In 1872, years before any
commercial installations, Anthony al-
ready hoped to acquire an “electromag-
netic machine for producing the elec-
tric light” to illuminate his lecture

room.7 The next year, as part of a wish
list of practical experiments for stu-
dents to perform in the laboratory he
did not have, Anthony included8
Electrical measurements. Mea-
surements of resistance and insu-
lation, power of batteries, location
of faults. Measurements of elec-
tromagnetic power, with reference
to electromagnetic machines and
motors.

The inclusion of motors was remarka-
bly farsighted, for in 1873 the develop-
ment of electric motors was barely
under way — for the most part in Eu-
rope.

The next year, unable to get a
Gramme dynamo from Europe, Anth-
ony built one with the help of a student
at Cornell and a machinist from Ithaca.
The machine was a tribute to Anth-

112

HISTORY OF PHYSICS

ony’s talent, and became an early
symbol of Cornell’s eminence in electri-
cal science. It was exhibited at the
Centennial Exhibition of 1876, and on
its return to the Ithaca campus it was
used to power two arc lights, wired
through underground cables of Anth-
ony’s design and manufacture. This
was the first such permanent installa-
tion in America. The dynamo was used
in the laboratory through the first
decades of the 20th century, and is still
in working condition today. By the
early 1880s, electricity was occupying
most of Anthony’s time. Mechanical
engineering undergraduates were writ-
ing theses on electrical topics under
Anthony’s supervision, and in early
1883 he was asked to draw up a
curriculum for an electrical engineer-
ing course. Approved by the trustees
and faculty, the course was offered that
fall in the physics department.

Cornell’s undergraduate degree pro-
gram in physics had been no more
popular than MIT’s. In the ten years
after 1876, only 13 students earned
physics degrees out of a total of 678
undergraduate degrees awarded at Cor-
nell. The student paper reported in
1876 that three-quarters of the under-
graduates in scientific courses planned
to be lawyers, physicians, ministers or
journalists; the rest teachers, mer-
chants or manufacturers, and “a very
few, scientists.” Although few students
pursued a physics degree, some physics
was required of nearly all students.
This was also true at MIT.

By 1880, Anthony was irritated by
crowding and the lack of laboratory
apparatus. He told officials at Cornell
that the department was “20 years
behind the times.”9 That year the
administration granted him his labora-
tory, and he requested a lecture room
with 200 seats. Ten years later, the

number of undergraduates in electrical
engineering numbered 218 — more than
could fit in the lecture hall at one time.

In 1885, Anthony built an enormous
tangent galvanometer, an instrument
of extraordinary precision and utility.
It represented the direction of the
department: After 1882, almost all of
Anthony’s requests for appropriations
concerned electrical apparatus. De-
fending one such a request in 1886, he
protested:10

Is it to be supposed that, in 1872, 1
should have foreseen the demand
that would be made by the extraor-
dinary growth and the vast impor-
tance of the industrial applications
of electricity? Is it to be wondered
at that I should see possible ways of
improvement now that I did not
see then?

Unfortunately for Anthony, the sym-
pathetic Andrew White had been suc-
ceeded as president in 1885 by the less
scientifically inclined Charles K. Ad-
ams, who would only later learn to
appreciate the place of technical stud-
ies in the university. Anthony’s 1886
request was denied — repeatedly. Frus-
trated, he left Cornell in 1887 to take a
position as consultant to an electrical
manufacturer.

He suggested as his successor Ed-
ward L. Nichols, who would become a
leader not only at Cornell, but in
American physics as well. Anthony
called him11

the best man I know to make a
success of the Physical Depart-
ment here in the directions both of
pure science and its practical ap-
plications.

Nichols was a Cornell graduate who
had spent four years in German labora-
tories, one year with Rowland, another
year with Edison, two years teaching in
Kentucky, and four years teaching at

the University of Kansas. In his last
year at Kansas, Nichols had prepared
an electrical engineering course for the
fall of 1887.

Nichols taught electrical engineer-
ing courses in his first year at Cornell.
In the spring of 1888, however, an
independent department was set up
within the Sibley College of Engineer-
ing, with an associate professor of
electrical engineering given responsi-
bility for teaching “the construction of
engineering work . . . peculiarly apper-
taining to electricity.” By the end of
the 1880s, the proper education of an
electrical engineer was beyond a phys-
ics department. The new programs
were run by electrical engineers with
practical experience and scientific so-
phistication. Even so, physics depart-
ments were required to teach young
electrical engineers the scientific fun-
damentals.

One of Anthony’s prize students had
just such training. Harris J. Ryan was a
member of the first formally admitted
class in electrical engineering and was
Anthony’s assistant. A year after his gra-
duation in 1887, Ryan became an instruc-
tor in physics, and later the principal fig-
ure in the electrical engineering
department.

Flourishing of EE

Although Cornell and MIT deserve
special attention for establishing two of
the earliest and most respected pro-
grams in electrical engineering, they
did not have the field to themselves for
long. In the same year that Cornell
introduced its program, 1883, the Ste-
vens Institute in Hoboken, New Jersey,
began a course in Applied Electricity.
A number of schools acknowledged the
rise of electricity with subcourses in
their physics departments — among
them Lehigh in 1883 and Rose Poly-

Class of 1890 electrical engineering graduates, in frock coats and a classic photograph of their halcyon days as students in a burgeoning
bowler hats, adorn stairs at MIT, then located in Boston’s Back Bay, for field. (Photo courtesy Archives, California Institute of Technology.)

SOCIAL CONTEXT

113

^ when electrician began to assume its
| modern meaning — someone who can
* wire a house or fix an appliance — and
o electrical engineers became more parti-
< cular about being called by their proper
title. Rowland and other prominent
physics professors — among them
George Barker at the University of
Pennsylvania, Henry Carhart at Michi-
gan, and Cyrus Brackett at Princeton —
had close ties to the commercial devel-
opment of electricity as consultants
and legal experts in patent squabbles.

Brooklyn Bridge, pictured just before its opening in 1883, became a symbol of American
ingenuity, heralding the new era of electricity with its many lights.

technic and the Lawrence Scientific
School at Harvard in 1884. The first
two were well-attended, but the Har-
vard program was little more than a
title in the catalog until the 1890s and
even then was weak. By that time,
electrical engineering programs exist-
ed in name, if not in fact, in schools
throughout the country.

At the 1884 International Electrical
Exhibition, Henry Rowland declared:
"It is not telegraph operators but elec-
trical engineers that the future de-
mands.” Accordingly, in 1886, he es-
tablished a program in applied
electricity at Johns Hopkins to train
electrical engineers, and enrolment
soon outgrew the new physics building.
But when Hopkins’s finances went sour
in the 1890s and no outside sponsor
could be found for the program, the
subject was withdrawn.

Interest in the new technology
reached into the Hopkins physics de-
partment itself. Rowland’s first PhD
recipient, William Jacques, given his
degree in 1879, went to work immedi-
ately for American Bell telephone com-
pany as an “expert,” a job that had not
existed when Hopkins had opened its
doors three years earlier. During the
1880s and 1890s, quite a few graduate
students were admitted to Rowland’s
laboratory with the express purpose of
gaining familiarity with electrical
science. Many of them left to work in
the industry. Rowland himself reigned
for two decades in a dual role as
America’s foremost pure physicist and
as America’s foremost electrician. In

the language of the day, “an electri-
cian ... is a person thoroughly ground-
ed in the theory of electricity and the
laws by which it is governed, but it is
not essential that he should have any
special knowledge of its practical appli-
cations beyond laboratory work.”12
This definition was provided in 1884 by
a trade journal in answer to a question
about the difference between an electri-
cian and an electrical engineer. In
practice, the distinctions were unclear
and largely semantic until the 1890s

Advancing truth and beauty

Besides stimulating departmental
growth in the schools, electricity gave
American physics research a utilitar-
ian justification it had never before
possessed. In 1876, at the time of the
founding of Johns Hopkins, the cham-
pions of American physics numbered a
mere handful. Besides those few physi-
cists lucky enough to be in teaching
positions or government service, the
supporters were found primarily
among the most educated in society.
This group prided themselves in up-
holding high standards of culture. For
them, those who pursued pure science
were somehow ennobled as the van-
guard of American civilization; they
considered the study of physics the
moral equivalent of the antebellum
study of the classics. The discipline of
the laboratory, enforced by Natural
Law, they argued, would replace the
discipline of conjugation and declen-
sion, enforced by the dusty pedant, and
the beauty of Nature’s Truth would
excel the beauty of Homer and Horace.
Although this group was also loud in
proclaiming that disinterested, pure
research was the basis of technological
advance, their hearts were in the battle
against the corruption and materialism
of the Gilded Age. But the practical
success of physics in the 1880s and
1890s was evident to all. Public and
industrial reliance on electricity and
the fortunes spawned by electrical pro-
ducts made the “physics as culture”
argument unnecessary and obsolete.

The passion for practicality — and the
concomitant lack of interest in the
development of theory — had long been
part of the American experience. Alex-
is de Tocqueville recognized this
American trait in the 1830s and de-
plored it, maintaining that hardly any-
one in the new nation was devoted to
pursuing knowledge for its own sake.
When John Tyndall lectured through
the eastern states in 1872-73, he made
a strong plea for the support of re-
search and implored Americans to
prove de Tocqueville wrong. In 1876,
the astronomer Simon Newcomb be-
moaned the nation’s pitiful contribu-
tions to abstract science. Thus, when
Henry Rowland stood before the phys-
ical science section of the AAAS in 1883

114

HISTORY OF PHYSICS

to deliver his celebrated “Plea for Pure
Science,” he was voicing frustrations of
long standing.

But Rowland, speaking after the
dawn of the Electrical Age, no longer
represented the majority of his collea-
gues. Most contemporary physicists
and their supporters welcomed the
opportunity electricity offered to dis-
play the fruits of their labors. Few
American physicists had the interest,
ability, and opportunity that enabled
Anthony and Cross to initiate electrical
studies in the 1870s. Yet a decade or
two later, virtually every physicist was
celebrating the virtues of electricity
and its applications. Maxwell, whom
Rowland revered, had acclaimed the
reversibility of the dynamo “the great-
est scientific discovery of the last
quarter of a century.”13 Within Row-
land’s immediate circle, Daniel Coit
Gilman, the president of Johns Hop-
kins, found in electricity a justification
for pure research. In an 1882 speech
about the role of university research in
the progress of civilization, Gilman
claimed14 that electricity had
wrought greater changes in com-
merce than the discovery of the
passage around the Cape; greater
modifications in domestic life than
any invention since the days of
Gutenberg . . .

Indeed, through the 1880s, Row-
land’s successors as vice-president of
the AAAS physical section either de-
picted the scientific mysteries of elec-
tricity or sang its praises as the gift of
physics to the world — or both. In 1887,
for example, William Anthony had
rebuked Rowland by celebrating the
patents taken by American physicists.
All but two of the patents were electri-
cal (and those two belonged to Row-
land). A. A. Michelson began his 1888
“Plea for Light Waves” with a glowing
description of the

wonderful achievements in the em-
ployment of electricity for almost
every imaginable purpose. Hardly
a problem suggests itself to the
fertile mind of the inventor or
investigator without suggesting or
demanding the application of elec-
tricity to its solution.

And in 1889, Henry Carhart, in his
“Review of Theories of Electrical Ac-
tion,” characterized for the decade the
utility of physics:

Of the practical applications of
electricity it is not necessary to
speak. They bear witness of them-
selves. A million electric lamps
nightly make more splendid the
lustrous name of Faraday; a mil-
lion messages daily over land and
under sea serve to emphasize the
value of Joseph Henry’s con-
tribution to modern civiliza-
tion. . . . The value of the purely
scientific work of such men is
attested by the resulting well-be-
ing, comfort and happiness of man-
kind.

Ironic turning point

The 1890s brought an ironic twist to
the relationship of physics and electri-
cal engineering in the US. By the end
of the decade, electrical engineering
educators complained that training in
a course administered by a university
physics department was bound to be
inadequate. They questioned the value
of abstract investigations in higher
physics and argued that the curriculum
should include only such physics as was
fundamental to engineering.

As the electrical engineers parted
company with the physicists, so did the
public. The utility of the physicists had
never been as clear to the general
public as it had been to the educators
and physicists themselves. In the
schools, electrical engineering attract-

ed new laboratories and substantial
funding. The research labs established
by General Electric, Westinghouse and
Bell Telephone were hailed by the press
and public. Physics, by contrast, did
not achieve significant academic or
public recognition until after World
War I, nor become preeminent among
the sciences until World War II.

References

1. J. K. Finch, A History of the School of
Engineering, Columbia University, Co-
lumbia U.P., New York (1954), page 68.

2. Background on MIT is in S. C. Prescott,
When MIT was Boston Tech, Technology
Press, Cambridge (1954); K. Wildes,
“Electrical Engineering at the Massa-
chusetts Institute of Technology,” un-
published manuscript, MIT Institute
Archives (1971). Student enrollment fig-
ures and course descriptions are in the
annual Catalogs.

3. W. C. Russel to A. D. White, 8 August
1872, A.D. White Papers (Collection 1/
2/2), Cornell University Archives (here-
inafter ADW).

4. Anthony to Russel, 30 June 1872, ADW

5. Anthony to White, September 1873,
ADW.

6. Anthony to C. K. Adams, 11 December

1886, Executive Committee Minutes
(Collection 2/5/5), Cornell University
Archives (hereinafter EC).

7. Anthony to White, 5 August 1872, ADW.

8. Anthony to White, September 1873,
ADW.

9. Anthony to Russel, 6 June 1880, ADW.

10. Anthony to Adams, 11 December 1886,
EC.

11. Anthony to Board of Trustees, 19 June

1887, EC.

12. The Electrician and Electrical Engineer
3 (April 1884) page 93.

13. Quoted in H. Greer, Popular Science
Monthly 24 (December 1883) page 254.

14. D. C. Gilman, President Gilman’s Ad-
dress at the Euclid Avenue Church, Fair-
banks, Cleveland, Ohio (1883) page 23. □

SOCIAL CONTEXT

115

Technological robot

benevolently embracing
Man at the entrance to
the Hall of Science at
the 1933 Chicago
Century of Progress
Exposition in the depths
of the depression.

Physics in the
Great Depression

Hard times raised hard questions
that were not answered in the 1930?s and
remain on the agenda now.

Charles Weiner physics today / October 1970

In the spirit of the soul-searching
seventies, physicists are now uneasily
questioning the pace of physics and its
proper place in society. They view
with foreboding the changes in slope of
the funding and employment curves
that, along with assessments of changes
in public attitudes, are the major social
indicators of the health of the physics
community. The immediate impact
and long-range threat of reduced re-
search funds, slackening employment
opportunities and lower public esteem
for physics are the apparent causes for
concern. Threatened or imminent hard
times are especially difficult to take on
the heels of the high expectations that
good times engender. This public
statement by a distinguished physicist
aptly characterizes the situation:

“Let us begin by facing the facts.
Physics has enjoyed a place in the sun
which it can not expect to hold per-
manently . . . Physicists would be
more than human if they were not
somewhat spoiled by the popularity
they have enjoyed.” 1

Charles Weiner is professor of History of
Science and Technology at MIT.

The need for analysis and planning was
brought to the attention of the physics
community by another leading physicist
in his presidential address to The Amer-
ican Physical Society.

“. . . this question of organized propa-
ganda for physics and a thorough in-
vestigation of the sociological aspects
of physics are the most important
problems confronting our society.
Physics in this country has simply
grown like Topsy, and, unless some
thought is given to these matters, we
may have an autopsy on our hands.” 2
These assessments of the state of US
physics, which certainly appear to fit
today’s scene, were made in the 1930’s.
The growth referred to took place in
the 1920’s, and the problems are those
of the depression. It should prove infor-
mative to look back into that decade to
see what gave rise to these statements
and how the physics community re-
sounded to them. Glimpses of an ear-
lier period can provide some perspec-
tive by showing the patterns of events
and by identifying some of the issues
and responses of the time. There is
also value in questioning the assump-
tions so often made about the pre-

World War II development of US
physics. These assumptions tend to
minimize the achievements of that era
as well as oversimplify its problems.

Coming of age in the twenties

The rapid growth of physics in the
US, referred to by Paul Foote in his
1933 presidential address to APS, had
occurred in the late 1920’s, when physi-
cists who were determined to build bet-
ter departments at universities through-
out the US received substantial finan-
cial support from private foundations.
The major source of support was the
Rockefeller-supported General Educa-
tion Board, which between 1925 and
1932 provided 19-million dollars to help
develop science departments in key US
universities. At the same time that
these efforts were being made, attention
was being given to increasing the com-
munication among US physics centers
as well as between them and European
centers. One of the most successful in-
novations was the establishment in
1919 of the National Research Fellow-
ships, which enabled outstanding new
US PhD’s to pursue postdoctoral work
at universities throughout the nation.

116

HISTORY OF PHYSICS

These fellowships were awarded by the
National Research Council with Rocke-
feller Foundation funds.

Many physicists, as is often noted,
went abroad to visit and to participate
in seminars and research at the major
European physics centers during the
late 1920’s, when the analytical force of
quantum mechanics was being tried on
a wide variety of physical problems.
Now forgotten is that, at the same time,
Europeans found the research facilities
at US universities increasingly desir-
able. For example, of the elite group of
135 European physicists who, from
1924 to 1930, received international
postdoctoral fellowships from the Rock-
efeller Foundation, one third chose to
study at US institutions; more of them
were attracted to the US than to any
other country. In addition, some of the
most distinguished European physicists
accepted invitations to lecture at US
universities in the late 1920’s and early
1930’s.

The annual University of Michigan
summer school for theoretical physics
was one of the special attractions for
Europeans and Americans. Begun in
1927 by department chairman Harrison
Randall, the school was famous for an
informal atmosphere that encouraged
lively discussion. The summer school
staff consisted of Michigan faculty and
invited lecturers, drawn from the ranks
of the best physicists in Europe and the

US. The high level of the staff can be
seen in this excerpt from a letter written
15 July 1930 to Gilbert N. Lewis by
young Joseph Mayer, a participant in
the 1930 summer school:

“[Paul] Ehrenfest, of course, rules
the whole symposium like a some-
what childish Tsar, but it is a won-
derful relief to hear quantum me-
chanics discussed with someone pres-
ent who will not permit empty math-
ematical symbols and words to pose
as explanations. For the first time
since I left Berkeley I’ve again expe-
rienced some of the clarity and liveli-
ness of the Monday evening collo-
quiums.

“[Enrico] Fermi is giving a course
on [P. A. M.] Dirac’s dispersion
theory, Ehrenfest an unnamed course
that so far has been the history of
physics in the nineteenth century,
and in addition there are two even-
ing colloquiums in theoretical
physics and one in experimental
every week. [Philip] Morse is giv-
ing an introduction to quantum
theory that I have not attended but
that is said to be good.

“Fermi, by the way, is a very young
and pleasant little Italian, with unend-
ing good humour, and a brilliant and
clear method of presenting what he
has to present in terrible English.” 3
Another innovation that demonstrates
the growth of the US physics communi-

ty was the establishment in 1928 of Re-
views of Modern Physics. John Tate,
editor of The Physical Review, asked 45
leading US physicists whether they
thought a review journal was needed in
the US. Edward Condon, who had re-
turned from his postdoctoral tom' of Eu-
rope a year earlier, was one of the many
who gave strong support to the idea.
In a letter to Tate, dated 2 October
1928, Condon said:

“I have been thinking ever since I re-
turned from Germany that the great-
est handicap to physical research
work here is the lack of an adequate
literature in English . . . There is no
question that our laboratories are bet-
ter now than those abroad, but we
lack tbe literature which brings the
young men quickly into step with the
research work in the various fields.” 4
The conscious effort to strengthen
physics departments and to improve
communication through personal inter-
action and professional journals pro-
duced a unique and vigorous physics
enterprise in the US. US institutions
were thus in close touch with contem-
porary work and were often in the fore-
front of many fields, as in the newly de-
veloping field of nuclear physics.

This new vigor was clearly in evi-
dence during the 1933 APS meetings,
which were held in Chicago to coincide
with the Century of Progress Exposi-
tion. John Slater, who was then chair-

At the University of Michigan summer
school in 1930. The informal group
discussion includes Maria Mayer
and Joseph Mayer, on the left, Lars
Onsager on the right, and Paul Ehrenfest
next to him. At the rear is Robert d’ E.
Atkinson. The lecturer in the other
photograph is Enrico Fermi.

man of the Massachusetts Institute of
Technology physics department, recalls
that what impressed him most was “not
so much the excellence of the invited
speakers, as the fact that the younger
American workers on the program gave
talks of such high quality on research of
such importance that, for the first time,
the European physicists present were
here to learn as much as to instruct.” 5

Impact of the depression

Physics in the US had grown rapidly
during the 1920’s and the physicists’ ex-
pectations were high. Then the de-
pression hit; its effects on the campuses
were felt gradually and had greatest im-
pact in the academic year beginning in
the fall of 1933. Younger men were
hurt most. In some departments junior
faculty were dropped, but the main

brunt was borne by the new PhD’s who
found it extremely difficult to get jobs.
Many subsisted on one small fellowship
after the other; others were able to find
assistantships that normally were given
to graduate students; still others left
physics. Faculty at the associate and
professorial level were least affected,
but they did receive salary cuts or “neg-
ative bonuses.” These cuts were slight-
ly offset by the decrease in the cost of
living, but they still hurt. A comment
from a letter written by Linus Pauling
to Samuel Goudsmit in May 1933 char-
acterizes the situation:

“I haven’t the faintest idea as to
where [your former student] can get
a job. Caltech is filled with our own
PhD’s and former National Research
Fellows hoping for a small stipend.
It is a shame these able men should
be without positions. We have had
only a 10% [salary] cut, a year ago,
but may well have another. I am
hoping that conditions will improve
soon.”

Or, to put it in the terms used by Foote
in December 1933:

“One does not require familiarity
with the matrix mechanics to under-
stand the principle of uncertainty as
regards a physicist’s employment
during the past three years.” 6
Financial support for science was
being severely reduced, and the outlook

1931 The NY Times Co

NOVEMBER 11, 1931

1933 NY Herald Tribune Co

SEPTEMBER 12, 1933

1934 The NY Times Co

MARCH 30, 1934

YIELDING TO SCIENCE

Of. A. H. Compton Visions New
Era in Physics When It Will
at Last Be Smashed.

BIG GENERATOR HINTS WAY

1,500,000 Volts Leap From $90
Device in Test Before the
American Institute.

The atomic nucleus, the storehouse
«( the vest energy of the atom, until
no* practically impenetrable by
ijencles controllable by science, has
tt lest begun to yield to experiments
*hich bid fair to disclose their In-
most nature, It was said last night
ty Dr. Arthur H. Compton of the
University of Chicago, Nobel Prise
winner In physics, at a dinner given
to identlsts and newspaper men by
•".e newly formed American Institute
Physics at the New York Athletic
jClub.

Experiments described by Dr. Comp-
'■»» as "remarkable," and achieving
what hed hitherto been regarded by
xuntists as impossible, recently

r

Atom-Powered
World Absurd,
Scientists Told

Lord Rutherford Scoffs at
Theory of Harnessing
Energy in Laboratories

Lord Rutherford

By The Atsnclaleu Press
LEICESTER, England. Sept. 11.—
Lord Rutherford, at whose Cambridge
laboratories atoms have been bom-
barded and split Into fragments, told
an audience of scientists today that
the Idea of releasing tremendous power
from within the atom was absurd.

He addressed the British Association
for the Advancement of Science in the
! same hall where the late Lord Kelvin
i asserted twenty-six years ago that the
j atom was indestructible.

Describing the shattering of atoms
by use of 5,000,000 volts of electricity,
Lord Rutherford discounted hopes ad-
vanced by some scientists that profit-
able power could be thus extracted.

"The energy produced by the break-
ing down of the atom Is a very poor
kind of thing,1' he said. "Any one who
expects a source of power from the
transformation of these atoms is talk-
ing moonshine. . . . We hope In
the next few years to get some Idea of j
what these atoms are, how they are I
: made and the way they sre worked." I
Sir Oliver Lodge, eminent physicist, i

USE OF THE ENERGY
IN ATOM HELD NEAR

1

Dr. Compton Says New Experi-
ments Show Its Practical
Use May Be Possible.

CITES SUCCESSFUL TEST

Found Expenditure of 100,000
Volts on Atomic Bombardment
Produced 3,000,000 Volts.

Science has obtained conclusive
proof from recent experiments that
the innermost citadel of matter, the
nucleus of the atom, can be
smashed, yielding tremendous
amounts of energy and probably
vast new stores of gold, radium and
other valuable minerals. Dr. Karl
T. Compton, president of the Mas-
sachusetts Institute of Technology,
declared last night before a meeting
of the Institute of Arts and Sci-
ences of Columbia University at
McMlllin Academic Theatre, Broad- §
way at 116th Street.

Although much energy must still
be used to bombard matter in order
to release atomic energy, the effi-
ciency of the process Is increasing
and there are hopeful signs that
eventual use of atomic energy on »
practical basis may be possible. Dr.

118

-

HISTORY OF PHYSICS

was dim. A survey of the congressional
appropriations bill by Science Service,
published in July 1932, showed that
funds for scientific research in the vari-
ous government departments had been
cut 12.5% for the 1932-33 fiscal year.
Further cuts were made by President
Herbert Hoover in the budget estimates
he submitted to Congress in December

1932. 7 Operating funds of the Nation-
al Bureau of Standards, the major gov-
ernment employer of physicists, were
effectively cut 70% between 1932 and

1934.8

The impact of budget cuts at the uni-
versities can be seen in these telling ex-
cerpts from F. Wheeler Loomis’s annual
reports for the University of Illinois
physics department, which, under his
leadership, had been among the depart-
ments making rapid strides in the pre-
ceding years:

1931-1932 “The outstanding fea-
ture of this year in the physics de-
partment, as probably in all others,
has been the curtailment of our ac-
tivities made necessary by the finan-
cial emergency in the University.
Since the time the economy orders
were promulgated in January the de-
partment will have saved out of its
appropriations about $3500, or 40
percent of the maintenance and oper-
ation budget for the year . . . most

severely affected will be, of course,
the research.”

1933- 1934 “The salient features of
the past year in the physics depart-
ment, have been the effects of the
depression budget and the reduced
enrollments in the courses. The de-
partment has had to get along with
half the operating funds it had in the
past and with no money at all for new
equipment.”

1934- 1935 “The department, whose

operating expenses have been re-
duced to a starvation point for over
three years, suffered a financial crisis
this winter and pretty nearly had to
close up . . . It is almost impossible to
convey an adequate idea of the ex-
tent to which our work, both in
teaching and research, has been ham-
pered and made inefficient and how
all progress has been blocked by the
inability to buy necessary articles.
We should have had pretty nearly to
cease activity in research if it hadn’t
been for the equipment which was
bought in our three boom years
1929-32 ” 9

The unfilled aspirations of budding
physicists and the despair of depart-
ment chairmen were amplified in public
statements by spokesmen for the scien-
tific community including William W.

Campbell, astronomer and president of
the National Academy of Sciences and
Karl T. Compton, chairman of the
board of the newly formed American
Institute of Physics. In 1934 Campbell
stressed that cutbacks in financial sup-
port of science had interrupted the ca-
reers of students and researchers and
that many of them would be lost to
science. The quality of research was
still good, but, he warned, if the re-
duced scale of support continued for
two or three more years, the results
would be very bad indeed.10 Comp-
ton and Henry Barton, director of AIR,
called for an increase in government
support of research to offset the decline
in private support. But, if scientific re-
search was to be supported by public
funds, then the public had to be in-
formed and convinced of the benefits of
research. Determined efforts to do this
were made by AIP.

Public image of physics

The public was not unaware of new
discoveries in physics, especially in nu-
clear physics, which promised to yield
new sources of energy. Newspapers
and magazines described the exciting
results of the “atom splitters,” including
artificial disintegration of the light ele-
ments and discovery of the neutron.
Despite Ernest Rutherford’s public ref-

© 1931 The NY Times Co

JUNE l 1931.

PHYSICS INSTITUTE
WILL BE ORGANIZED

Dr. K. T. Compton, Head' of M.
I. T., Announces Plan to Knit
All Branches in Field.

SOCIETY WILL SERVE PUBLIC

Pre»« Department to Explain New
Laboratory Dlaeoveriea at
They Occur.

CAMBRIDGE, Mail., June 3 UP).-
Plant for formation of a consolidated
scientific organization to be known
as the American Institute of Physics
were made public today by Dr. Karl
T. Compton, president of Massachu-
setts Institute of Technology.

Both science and the public are to
be served. The institute will bring
together several scientific organisa-
tions now separate but having com-
mon interests. It will also knit to-
; gether a great group of men in in-
dustrial laboratories and manufactur-
ing plants who, as physicists, play a
most fundamental role in modern in-
dustry, but who have not heretofore
constituted a well recognized unit.
Also in schools and colleges, local or
student branches of the institute may-
be founded.

© 1934 The NY Times Co

1935 The NY Times Co

etor jfork ®

Copyright. 1934, by The New Tork Times Company.

NEW YORK, FRIDAY, FEBRUARY 23, 1934~

Leaders Deny Science Cuts Jobs;
Warn Against * Research Holiday *

Dr. Millikan Declares Technological Unemployment Is a Myth —
Compton Proposes Federal Subsidies for Invention —
Roosevelt Aids All-Day Symposium Here.

Science struck back at its critics
yesterday, and with the aid of some
of its inventions— the radio, sound
cameras and loud-speakers— it told
the world that science makes jobs
and does not end them.

Fortified with statistics to con-
found the technocrats, armed with
a message from the President, and
bearing determined and bulky state-

tries" in the near future and make
many jobs.

The electron, he pointed out, had
"gotten into industry” and had
"created jobs" in enormous num-
bers, and research in pure and ap-
plied science undoubtedly would
produce other brain children that,
when harnessed, would make indus-
tries and provide jobs for thou-

NOVEMBER 28, 193

DRCONANT oppose
CURB ON RESEARC

‘Planning’ of Science Wou
Check Intellectual Activity
Harvard President Says.

PRAISES CARNEGIE METHO

Free Hand for Exceptional Mai
Urged — Dr. Keppel Sees Big
Trusts Facing Changes.

Dr. James B. Conant, presidei
of Harvard University, took issue
last night with the theory tbi
brakes should be put upon the in
crease of scientific research an
knowledge. He spoke at a dinn«
In the Waldorf-Astoria Hotel, en<
lng the centenary celebration o
Andrew Carnegie's birthday.

The dinner was given by the C
negie Corporation of New York,
which has had charge of the cen*
tennial celebration in the Unite
States and the British dominions
Tf wo« bv members of th

SOCIAL CONTEXT

119

utation of the idea that tremendous
amounts of energy could be released
from the atom and harnessed, many sci-
entists, science writers and laymen ea-
gerly discussed the possibilities.
Rutherford’s statement has been fre-
quently quoted in recent years:

“The energy produced by the atom is
a very poor kind of thing. Anyone
who expects a source of power
from the transformation of these
atoms is talking moonshine. . . 11

Less well known now are the more op-
timistic views of other physicists. At-
tached to the New York Herald Tribune
account of Rutherford’s talk was anoth-
er news item quoting Ernest Lawrence
on the need to develop an efficient
method of obtaining atomic power.
Lawrence concluded: “I have no opin-
ion as to whether it can ever be done,
but we’re going to keep on trying to do

it.” 12

Despite the disagreement among sci-
entists, public interest in atomic energy
was high in the early 1930’s. But al-
though the public often associated the
physicist with expectations of practical
applications of atomic energy, it also in-
creasingly linked him with unfamiliar
complexities. Mingled with headlines
such as “Use of tbe Energy in Atom
Held Near,” were such editorial com-
ments as:

“It is not the electron that needs
seven dimensions but the mathe-
maticians. The world awaits an-
other Newton to reveal simplicity.
We are merely in the stage of ex-
perimenting with theories. Out of
it clarity must issue if science is
not to become irrational.”13
In 1934, commenting on the complexity
of the neutrino concept, the Times
asked: “Can it be that nature needs
eight particles in constructing the cos-
mos? Or is it the physicists who need
them.” 14

Antiscience movement

More significant than the ambivalent
public image of physics in the early
1930’s was the changing public attitude
towards science in general. As the de-
pression wore on there was an increas-
ing disenchantment with the “techno-
logical progress” that had long been as-
sociated with science. Science-based
technology and the labor-saving devices
it had produced were variously seen as
uncontrolled, unplanned or misappro-
priated and, in all cases, as a major fac-
tor in the deepening economic crisis
and the resulting despair. One pro-
posed solution was to declare a morato-
rium on scientific research. The “Stop
Science” movement dated back to the
late 1920’s in England and found in-
creased social resonance in the US in
the early 1930’s. It is difficult to deter-
mine how widespread this attitude was,
because it was only occasionally articu-

lated. It was, however, perceived as a
major threat by leaders of the scientific
community, because it occurred at pre-
cisely the time when scientists needed
to make an effective case for increased
public support.

Even before the economic crisis, criti-
cism of science was gaining ground
among those who saw it as a threat to
humanistic values. Late in 1928, Rob-
ert A. Millikan commented on “the cur-
rent opposition to the advance of
science,” and told his Chamber of Com-
merce audience that the real question
was “how the forward march of pure
science, and of applied science which
necessarily follows upon its heels, can
best be maintained and stimulated.” 15
By mid-1932, the realities of the de-
pression sharpened the criticism of
science and modified the response. In
a speech dedicating the Hall of Science
for the Chicago Century of Progress Ex-
position, Frank B. Jewett, head of the
Bell Telephone Laboratories noted:

“In some quarters a senseless fear of
science seems to have taken hold.
We hear the cry that there should be
a holiday in scientific research and in
the new applications of science, or
that there should be a forced stop-
page in the extension of old usages
by mandatory legislation.” 16
Jewett’s response was a call for greater
efforts to weave science into the social
structure. The purpose of the Century
of Progress Exposition, he said, was to
increase understanding of the real place
of science in the social structure and of
those factors that have their roots in
science and must influence the course
of social controls in the years ahead.

Science was the theme of the exposi-
tion. Chicago was celebrating her cen-
tenary as a city, and the planners of the
exposition wanted to show that the
city’s growth had been united with the
growth of science and industry during
the preceding century. The National
Research Council enlisted the support of
400 scientists and businessmen to ad-
vise on exhibits. During the three years
preceding the opening of the exposi-
tion, about 90 physics exhibits were
devised and assembled by a group of
physicists under the direction of Henry
Crew. Similar exhibits represented the
other sciences.

The exposition itself was opened in a
dazzling manner to emphasize the ac-
complishments of science. Light that
had ostensibly started its journey to
earth from the star Arcturus 40 years
earlier (at the time of the last great
Chicago exposition) was relayed to Chi-
cago from the 40-inch refracting tele-
scope at Yerkes Observatory, Wiscon-
sin, in the form of an electrical im-
pulse to start the big show’s night
life. (The distance to Arcturus is now
known to be about 36 light years.) The
guidebook put it this way:

“A miracle, they would have said a
hundred or even forty years ago.
But today, the ‘electric eye,’ relays,
vacuum tubes, amplifiers, micro-
phones, which respond to the tiniest
fluxes of energy, help to do the work
of the world in almost routine man-
ner. Progress!” 17

The exuberant celebration of science
and its applications took place in one of
the worst depression years, and a major
aim was to demonstrate that “the steady
march of progress” could not be
stopped by temporary “recessions.”
Considering the large number of unem-
ployed in 1933, one wonders how the
fair-going public reacted to the slo-
gan boldly proclaimed in the official
guidebook: Science Finds— Industry

Applies— Man Conforms! 18 The use of
science at the exposition may have been
imaginative and entertaining, but it
provided no real answer to critics who
called for a research holiday. Instead it
provided a dramatic reaffirmation of
the relation of science to a technology
that, in the eyes of some critics, had
been misdirected and thus had contrib-
uted to existing social evils.

Response of the physicists

By late 1933 leaders of the physics
community were alarmed about the
criticism of science, because such criti-
cism threatened to reduce public sup-
port of research even further. Their
approach was to deny that science had
caused unemployment. On the con-
trary, they asserted, science had created
more jobs, and greater support of
science could help to end the depres-
sion. Barton was among those who
called for more flexible political and
economic institutions and for methods to
cope with “natural and unavoidable in-
creases in human knowledge,” 19 but
the major emphasis of the scientists’ re-
sponse was simply that the answer was
more rather than less science.

AIP and the New York Electrical So-
ciety (an engineer’s group) responded
to the crisis by conducting a well publi-
cized symposium, “Science Makes More
Jobs,” in February 1934. Speakers in-
cluded Karl T. Compton (who was
president of MIT as well as chairman of
the AIP Board of Governors), Millikan
(president of the California Institute of
Technology), Frank Jewett and Wil-
liam Coolidge (director of the General
Electric Research Laboratory). Their
talks, urging continued support of scien-
tific research by government, universi-
ties and industry, were broadcast na-
tionwide. Letters were read from Pres-
ident Franklin D. Roosevelt and from
Albert Einstein, who pointed out:

“. . . one cannot be sufficiently
cautioned against the attempt to
economize on scientific work. On
the one hand, the progress of impor-
tant branches of technology depends

Visitors in the Hall of
Science at the 1933
Century of Progress
Exposition. This
photograph and the
one on page 31 are
used by permission of
the Library, University
of Illinois, Chicago
Circle Campus.

on the results of experimental and
even of theoretical science; and on
the other, each disruption of scientif-
ic work causes lasting damage to the
living body of research; that is to say,
a partial forfeiture of previously ex-
pended labor and capital. . . . Hence,
it is in the interest of this country to
put on a secure footing the continua-
tion of scientific investigations on the
previous scale . . . .” 20
The symposium was not unnoticed. A
front page article in The New York
Times the next day began “Science
struck back at its critics yesterday . .
and a full account of the meeting and
the major points of the speeches fol-
lowed. The editorial page, however,
expressed disappointment:

“Neither the statistics nor the argu-
ment are new. Nor did any of the
protagonists of the laboratory explain
why there is poverty amid plenty,
and idleness where we expect to hear
the hum of the machine. We look to
them for a way out of the slough,
only to find them as helpless as the
economists. As yet no one has de-
vised the means of absorbing new
technical developments with the least
possible amount of distress. The
question of pace is all important.”21
The editorial went on to call for a gov-
ernment plan to apply science without
neglecting “human aspirations” and
“moral values.”

The scientists simply had not ad-
dressed themselves to the immediately
relevant questions of the social manage-
ment of science and its applications.
They had assumed that science and
technology were the sources of progress

that would lead to desirable improve-
ments in the social condition. Al-
though the tone was more defensive
than the slogans of the Century of Prog-
ress Exposition, the message was the
same. No wonder then, that even some
friends of science tended to discount
the scientists’ statements as special
pleading.

While science was attempting to an-
swer its critics, efforts were also under-
way in Washington to improve coordi-
nation of government scientific work
and to develop an emergency scientific
program to combat the depression.
Karl Compton was chairman of the
Science Advisory Board appointed by
President Roosevelt in 1933. Compton
emphasized the need for major govern-
ment support of applied science; some
of the money could then be used to
support basic science. His theme was
expressed in the title of an article he
wrote in 1935: “Put Science to Work:
The Public Welfare Demands a Na-
tional Scientific Program.” 22 To bol-
ster his point that science should have
greater, rather than less, government
support, he argued that other nations
had more enlightened policies toward
the support and organization of re-
search. But the Board’s activities were
often marked by disagreements about
the relative roles of the social and natu-
ral sciences. Another major roadblock
was the fear of many scientists that gov-
ernment support would lead to govern-
ment control and to the involvement of
science in political and social issues.
The Board went out of existence in
1935, and all concerned agreed that it
had been a failure.23

In general, the arguments used dur-
ing the early 1930’s to encourage great-
er moral and financial support of
science by the public went wide of the
mark. It was not enough merely to
reassert that the basic science-applied
science-technology cycle would allevi-
ate the economic and social crisis. In
answering their critics, scientists did not
respond adequately to the public’s fear
that uncontrolled and misapplied tech-
nology caused human misery. Karl
Compton and others did urge individual
scientists to analyze social, economic
and political problems, and to ask at
what points science could be usefully
brought to bear on them.24 But
spokesmen for the US science commu-
nity appeared reluctant to deal publicly
with the social and political issues in-
volved in revamping institutions and in
discussing the rate and direction of the
application of science. Justifying pub-
lic support of science as a social good,
however, implicitly involved assump-
tions about the social processes leading
to eventual application of research. To
ignore the growing concern with the
need to analyze and improve these so-
cial processes was to weaken the argu-
ment for support of science.

The problem disappears

Things got better anyway. After
1935 the financial pinch eased and
more academic teaching jobs became
available; young physicists were needed
to cope with the increasing enrollments
in US colleges and universities. The
improvement was only gradual, how-
ever, and in the middle and late 1930’s
the search for employment took many

SOCIAL CONTEXT

121

physicists into work they had not pre-
viously considered (for example, into
oil fields as part of industrial geophysi-
cal research teams). A major effort
was made by AIP during this period to
call attention to the role of physics in
industry, and symposia were held
throughout the country to explore how
this role could be increased for the ben-
efit of industry, the nation and the
physicists. These efforts raised occa-
sional questions about whether the new
physics PhD’s were properly prepared
and motivated for industrial positions,
but apparently no major change in
physics education resulted.26

Bv the end of the 1930’s, growth
curves looked good again. More than
1400 physics doctorates were awarded
by US universities from 1931 to 1940,
double the number awarded in the pre-
ceding decade.26 The physics profes-
sion in the US had also been enriched
by about 100 very talented physicists
who had emigrated from Europe be-
cause they were unable or unwilling to
continue their careers in Nazi-domi-
nated countries.27 By the spring of
1941 an estimated 4600 physicists were
at work in the US, about half of them
with doctorates,28 and total expen-
ditures for scientific research in the US
had doubled during the decade.29 De-
spite the depression crisis, physics had
recovered and normal “progress” had
returned.

During the dismal depression days
questions about the internal dynamics
of the physics community and about its
relationship with the larger society were
raised. These questions remained un-
answered, to emerge again in other
times of crisis. Although the vast
changes that have occurred since the
1930’s in physics, in the physics com-
munity and in the role of physicists in
society have been accompanied by new

questions and problems, the continuity of
certain issues is clear. The perspective
provided by the experiences of the
depression emphasizes the pressing need
and new opportunity to make (borrowing
Foote’s 1933 phrase) “a thorough investi-
gation of the sociological aspects of phys-
ics.” In the 1930’s adequate answers were
not provided to the challenges to the so-
cial relevance and human implications of
physics, because significant changes in
the economic and political situation per-
mitted resumption of the growth of phys-
ics. But physicists now have another
chance to respond, and they must if they
are to cope with the present crisis and
plan for the future.

References

1. A. W. Hull, “Putting Physics to Work,”

Rev. Sci. Instr. 6, 377 (1935).

2. P. Foote, “Industrial Physics,” Rev. Sci.
Instr. 5, 63 (1934).

3. Lewis Papers, University of California,
Berkeley.

4. Niels Bohr Library, AIP.

5. J. C. Slater, “Quantum Physics in
America Between the Wars,” physics
today 21, no. 1, 43 ( 1968).

6. P. Foote, Ref. 2, page 57.

7. Science 76, 94 and 561 (1932).

8. R. C. Cochrane, Measures for Progress:
A History of the National Bureau of
Standards, US Dept of Commerce,
Washington, D. C., ( 1966) page 322.

9. G. M. Almy, “Life with Wheeler
[Loomis] in the Physics Department,
1929-40,” manuscript, Niels Bohr Li-
brary, AIP.

10. W. W. Campbell, Science 79, 391
(1934).

11. H. A. Barton, “Scientific Research in
Need of Funds,” Literary Digest 119,
18 (1935).

12. New York Herald Tribune, 12 Sept.
1933.

13. The New York Times, 25 June 1933.

14. The New York Times, 11 March 1934.

15. R. A. Millikan, “Relation of Science to
Industry,” Science 69, 30 (1929).

16. F. B. Jewett, “Social Effects of Modern
Science,” Science 76, 24 ( 1932 ) .

17. Chicago Century of Progress Inter-
national Exposition, Official Guide
Book of the Fair, page 20, Chicago
(1933); L. Tozer, “A Century of
Progress, 1833-1933: Technology’s
Triumph Over Man,” American Quar-
terly 4, 78 (1952).

18. Official Guide Book of the Fair, page
11.

19. H. A. Barton, “Shall We Stop Scien-
tific Progress,” Rev. Sci. Instr. 4, 520
(1933).

20. A. Einstein to H. A. Barton, 21 Feb.
1934. Niels Bohr Library, AIP; talks
published in Scientific Monthly 38,
297 (1934).

21. The New York Times, 24 Feb. 1934.

22. K. T. Compton, The Technology Re-
view 37, 133, 152 (1935),

23. A. H. Dupree, Science in the Federal
Government: A History of Policies
and Activities to 1940, Harvard U. P.,
Cambridge ( 1957 ) page 350.

24. K. T. Compton, “Science and Pros-
perity” Science 80, 387 (1934).

25. Physics in Industry, AIP, New York
(1937).

26. National Research Council publica-
tions and Dissertations in Physics
(M. L. Marckworth, ed. ), Stanford
(1961).

27. C. Weiner, “A New Site for the
Seminar: The Refugees and Ameri-
can Physics in the Thirties,” in In-
tellectual Migration (D. Fleming and
B. Bailyn, eds.), Harvard U. P., Cam-
bridge, Mass. (1969), page 190.

28. “Physicists in National Defense,”
mimeographed report, April 1942,
Niels Bohr Library, AIP.

29. V. Bush, Science the Endless Frontier,

Washington, D. C. (1945), page 86.
(Reprinted by National Science Foun-
dation, 1960). □

!

SOCIAL CONTEXT

123

Scientists with a secret

While the Nazi war machine was gearing up, a few physicists
realized that a fission chain reaction was feasible — would they be able
to get all groups to agree to hold back publication?

Spencer R. Weart

What are physicists to do if they make a
discovery that promises to transform
industry but also threatens to revolu-
tionize warfare? Should they investi-
gate the phenomenon within their tra-
ditions of free and open inquiry or keep
the deadly secret to themselves? This
is the dilemma that was faced by sever-
al groups of physicists who studied ura-
nium fission in 1939 and 1940. In the
spring of 1939 one group, foreseeing the
unprecedented power of nuclear weap-
ons, made a concerted attempt to re-
strict knowledge of chain reactions.
But it was not until over a year later
that censorship — imposed by the com-
munity of physicists on itself — became
fairly complete.

Any attempt to keep a secret must by
its very nature follow a course that is
difficult to observe, creating confusion
and misunderstanding. But this
course, which the participants could not
see clearly at the time, can now be
pieced together from collections of pa-
pers made available to researchers, sup-
plemented by oral history interviews
conducted by the Center for History of
Physics of the American Institute of
Physics.

Fears of disaster

The first arguments over nuclear se-
crecy revolved around the unlikely fig-
ure of Leo Szilard. A short, round, exu-
berant Hungarian, Szilard in 1939 had

Spencer R. Weart is the director of the Center
for History of Physics, American Institute of
Physics, New York.

neither a job nor a home. But he was
uniquely qualified to face the issues of
nuclear energy and secrecy because for
over five years he — and he alone — had
been concentrating on these problems.

Since 1933 Szilard, then recently ar-
rived in England to escape the Nazi
persecution of Jews, had wondered if
there was a way to release the energy
that physicists knew to be bound up in
nuclei.1 The answer came with his re-
alization that if one could bombard
some element with a particle (say, a
neutron) and make it radioactive in
such a way that it emitted two particles,
a chain reaction of awesome power
might be induced. The possibility
seemed much closer the next year, when
Frederic Joliot and his wife Irene Curie,
working at the Radium Institute in
Paris, discovered that, with alpha parti-
cles, one could indeed make nuclei ra-
dioactive artificially. Szilard decided
to devote himself to nuclear physics and
set out to search for some type of nucle-
us in which a chain reaction might be
sustained.

From the start Szilard feared the con-
sequences of his work. He attempted
to gain some control by the only means
then available to a scientist who wanted
to restrict the use made of his work:
He took out a patent on his ideas. Fur-
thermore, he persuaded the British gov-
ernment to declare the patent secret;
there was a small but real possibility, he
warned them, of constructing “explo-
sive bodies . . . very many thousand
times more powerful than ordinary
bombs.”2 Meanwhile Szilard brashly

PHYSICS TODAY / FEBRUARY 1976

tried to alert his colleagues in Britain.
His ideas, he told one professor in 1935,
could cause an industrial revolution but
might cause a disaster first. It would
be necessary to bring about something
like a conspiracy of the scientists work-
ing in the general field. In a letter to F.
A. Lindemann, the head of physics at
Oxford, he offered a mechanism to en-
sure secrecy — an agreement to make ex-
perimental results in the dangerous
zone available only to those working in
nuclear physics in England, America
and perhaps one or two other countries,
while otherwise keeping quiet.3

Szilard foresaw only too well the like-
ly reaction to his efforts: “Unfortu-
nately it will appear to many people
premature to take some action until it
will be too late to take any action.”3
And indeed the leading physicists in
Britain were cool to Szilard’s obstreper-
ous advice. They thought his proposed
chain reaction entirely unworkable (as
was in fact the case for the mechanisms
Szilard was then considering). They
were suspicious when he sought to pat-
ent his ideas, suspecting that he was
seeking pecuniary return, a motive in-
compatible with British traditions of
disinterested science. Finally, they
found the idea of scientific secrecy en-
tirely alien. Even those scientists who
felt most keenly the responsibility of
scientists for the consequences of their
discoveries traditionally felt that secre-
cy is abhorrent and that interference
with the normal process of open criti-
cism would not only impede scientific
progress but pervert it.4’5

124

Szilard went on to study various ele-
ments for a possible chain-reaction
mechanism; he had not quite reached
uranium when he learned that Otto
Hahn, Fritz Strassmann, Otto Frisch
and Lise Meitner had discovered urani-
um fission. When Szilard heard of this
in January 1939 in New York, where he
had moved to escape the war that ap-
peared ever more imminent in Europe,
he discussed his concern with scientists
at Columbia University.

Private messages

The leading nuclear physicist there
was Enrico Fermi, who had fled Italy
because Fascist race laws affected his
Jewish wife, and who had arrived in
New York scarcely three weeks ahead of
the news of the discovery of fission.
Like Szilard and other physicists, Fermi
quickly recognized the possibilities this
discovery opened. According to one ac-
count, he made a rough calculation of
the size of the hole a kilogram of urani-
um would make in Manhattan Island if
it underwent an explosive chain reac-
tion.6 However, he soon concluded
that this would never happen: When a
uranium nucleus was struck by a neu-
tron and split in two, it seemed unlikely
that it would release enough neutrons
to sustain a chain reaction. When Szil-
ard approached Fermi about the need
to keep fission work secret, Fermi’s re-
sponse was direct: “Nuts!”

From the very beginning [Szilard re-
called] the line was drawn; the differ-
ence between Fermi’s position
throughout this and mine was
marked on the first day we talked
about it. We both wanted to be con-
servative, but Fermi thought that the
conservative thing was to play down
the possibility that this [chain reac-
tion] might happen, and I thought
the conservative thing was to assume
that it would happen and take all the
necessary precautions.1
Rebuffed by Fermi, Szilard remained
alert for a way to control events. At
about this time, late January, a tele-
gram arrived at Columbia, addressed
from Hans Halban, a physicist in Paris,
to his colleague George Placzek. As
Szilard recalled it long after, the tele-
gram was opened by a secretary by mis-
take, and Szilard learned the contents:
“JOLIOT’S EXPERIMENTS SECRET.”
Placzek had just come from a visit in
Paris, and Szilard assumed that Placzek
had learned of an experiment Joliot was
doing; apparently Joliot had now decid-
ed to keep the experiment quiet for the
time being. Szilard had little doubt
what experiment would be so important
as to require secrecy.

What Szilard felt was involved here
was the sort of secrecy that had been
traditional in science for centuries — the
caution of the scientist who holds back
his results until he is ready to publish

HISTORY OF PHYSICS

them, so they will not be broadcast in a
distorted form and so that others will
not take advantage of a hint to beat him
to the next result. This was quite dif-
ferent from the sort of secrecy Szilard
had in mind. There was some misun-
derstanding here, for Joliot did not ac-
tually begin fission experiments until
late January, after Placzek had left
Paris, and it is not clear what Halban
and Placzek were corresponding about.
But Szilard now believed (correctly as it
happened) that Joliot’s group was
working on fission, and decided to send
him a letter.

The only reason he was writing, Szil-
ard said, was that there was a remote
possibility that he would be sending a
cable after some weeks, and the letter
was to explain what his cable would be
about. Some scientists in New York
were concerned about the possibility
that neutrons would be liberated in fis-
sion. Obviously, if more than one neu-
tron would be liberated, a sort of chain
reaction would be possible. In certain
circumstances this might then lead to
the construction of bombs which would
be extremely dangerous in general and
particularly in the hands of certain gov-
ernments. Perhaps steps should be
taken to prevent anything on this
subject from being published. No defi-
nite conclusions had been reached, but
if and when any steps were agreed on,
Szilard would cable Joliot. Meanwhile
Fermi was doing experiments to see
whether the danger was real, and these
would perhaps be the first to give reli-
able results. But if Joliot got definite
results sooner, Szilard would be glad to
have the uncertainty ended. Also, if
Joliot felt that secrecy should be im-
posed, his opinions would be given very
serious consideration.3

Neither Joliot nor his close collabora-
tors Halban and Lew Kowarski re-
sponded. The letter was obviously a
purely personal venture, and this im-
pression must have been reinforced by a
letter Fermi sent Joliot two days later.
On 4 February 1939 Fermi wrote that
he was then engaged in trying to under-
stand what was going on in uranium fis-
sion— as was, he thought, every nuclear
physics laboratory. After thus inform-
ing Joliot’s team that they had competi-
tion, Fermi went on to ask help for an-
other Italian refugee scientist and
closed without saying a word about
keeping secrets.7 There was every rea-
son to believe that Fermi would publish
first if the French held back their own
results.

Even as a personal request Szilard’s
letter made little impression on the
French, for it stated that it was only
meant to help them understand a cable
that might follow. Weeks passed, no
cable appeared, and the French, as
Kowarski recalled, “considered that
probably the whole idea was aban-
doned. We simply published.”8

This publication, the first result of
the joint efforts of Halban, Joliot and
Kowarski, contained important news:
Neutrons were indeed liberated when a
uranium nucleus fissioned.9 The ex-
periment was of a kind that would only
have been done in a few places, requir-
ing ingenuity, a powerful source of ra-
dioactivity and an interest in chain re-
actions. It had not been easy to detect
the few neutrons produced in fission
amidst the flood of neutrons that had
been required to provoke some fissions
in the first place, nor had it been ob-
vious that these neutrons were impor-
tant. Although the French, like Fermi,
believed scientists everywhere were

The many “secrets” of the atomic bomb

There was no single discovery that showed how

atomic bombs could be built, but a combination of discoveries

made at various times. Here is a partial list:

Published discoveries Unpublished discoveries

1934 Artificial radioactivity can be pro-
duced with alpha particles (Joliot and
Curie, France) or neutrons (Fermi, Italy).

December 1938 Neutrons can cause ura-
nium to fission (Hahn and Strassmann,
Germany, Frisch, Denmark and Meitner,
Sweden).

March 1939

► Neutrons are produced during fission
(Anderson, Fermi and Hanstein, US;
Szilard and Zinn, US; Halban, Joliot and
Kowarski, France).

► Two or three neutrons are emitted per
fission (same groups).

► U236 is the fissionable isotope of urani-
um (Bohr and Wheeler, US).

June 1939-February 1940 A self-sustain-
ing nuclear reactor can be built if a suit-
able moderator can be found (Szilard,
US; Halban, Joliot, Kowarski and Perrin,
France; Heisenberg, Germany; various
groups, USSR).

Spring 1940

► Carbon is a suitable moderator for a nu-
clear reactor (Anderson and Fermi, US).

► Nuclear reactors can be used to pro-
duce a fissionable element, plutonium
(Turner, US) — from this resulted the
bomb that devastated Nagasaki.

► It is possible to isolate sufficient U235 to
make an explosive critical mass (Frisch
and Peierls, UK) — from this resulted the
bomb that devastated Hiroshima.

125

-

SOCIAL CONTEXT

hard at work on the question, there was
in fact only one other group then carry-
ing on a similar experiment — the group
at Columbia.

Chain reaction — and invasion

By mid-March Fermi and Szilard,
working with Herbert Anderson, Walter
Zinn and others, had done their own ex-
periments and independently learned
the distressing news that neutrons were
produced in fission. This was still far
from proving that a chain reaction was
possible, for that would depend on the
precise number of neutrons emitted in
each fission, a thing still more difficult
to measure. The group estimated that
there were about two neutrons per fis-
sion, which made it appear only barely
possible that a chain reaction could be
sustained (the true value is about 2.5
neutrons per fission).

On 15 March, as the Columbia physi-
cists finished writing up their experi-
ments for publication, German troops
invaded the remnant of Czechoslovakia
that had survived the Munich agree-
ment. With this action, many felt,
Hitler crossed his Rubicon, subjecting
for the first time a non-German people
and giving a clear signal that world war
was inevitable. Despite their concern
over this, the physicists sent their pa-
pers to the Physical Review the next
day.

Szilard was not satisfied, and three
days later he met with Fermi and with
another Hungarian refugee physicist,
Edward Teller. As Szilard recalled the
meeting, he and Teller pressed for
keeping their work secret, but Fermi
was repelled by this idea, holding that
publication was basic to scientific mo-
rality. “But after a long discussion,
Fermi took the position that after all
this is a democracy; if the majority was
against publication he would abide by
the wish of the majority . . -”1 Fermi
therefore arranged to ask the Physical
Review to delay the publication indefi-
nitely.

Szilard was now on the point of ca-
bling Joliot, but before he did so he
heard of the French team’s note, just
published in Nature, which revealed
that some neutrons are emitted in fis-
sion. Fermi felt that there was now no
secret to keep, so that there was no
longer any sense in refusing to publish.
Szilard denied this (the crucial number
of neutrons emitted per fission was not
yet published), and argued that “If we
persisted in not publishing, Joliot would
have to come around; otherwise, he
would be at a disadvantage, because we
could know his results and he would not
know our results.” Fermi was not con-
vinced but, determined to be fair, he re-
luctantly agreed to put the matter be-
fore George Pegram, administrative pa-
tron of the Columbia group and a re-
spected physicist. Pegram delayed his

WIDE WORLD

SZILARD

KOWARSKI, HALBAN AND JOLIOT

CURIE LABORATORY

126

HISTORY OF PHYSICS

NATIONAL ARCHIVES

FERMI

decision for some time. Szilard’s argu-
ments were forceful, but others at Co-
lumbia replied that an attempt to re-
strict publication was both futile and an
undesirable breach of scientific cus-
tom.1’3

Warnings

While Pegram deliberated, Szilard
and his friends were determined to
waste no time. Several of them talked
the matter over, among them Victor
Weisskopf, an emigre Austrian physi-
cist. “We were very much afraid of the
Nazis,” Weisskopf recalled. “We knew
this was a hopeless thing but we
thought we had to try . . . And then the
question was . . . how do we get to Jol-
iot.” As Weisskopf said in a recent in-
terview, he had met Joliot’s collaborator
Halban years earlier and the two had
become close personal friends, so Szil-
ard and Weisskopf drafted a telegram
to Halban, which Weisskopf signed.
The telegram asked Halban to advise
Joliot that papers on neutron emission
had already been sent to the Physical
Review, but that the authors had agreed
to delay publication for the reasons in-
dicated in Szilard’s letter to Joliot of 2
February. The telegram continued:

NEWS FROM JOLIOT WHETHER HE
IS WILLING SIMILARLY TO DELAY
PUBLICATION OF RESULTS UNTIL
FURTHER NOTICE WOULD BE WEL-
COME STOP IT IS SUGGESTED THAT
PAPERS BE SENT TO PERIODICALS
AS USUAL BUT PRINTING BE DE-
LAYED UNTIL IT IS CERTAIN THAT
NO HARMFUL CONSEQUENCES TO
BE FEARED STOP RESULTS WOULD
BE COMMUNICATED IN MANU-
SCRIPTS TO COOPERATING LABORA-
TORIES IN AMERICA ENGLAND
FRANCE AND DENMARK . . ?

The proposed scheme was similar to the
one Szilard had conceived in 1935, with
the additional idea that papers should
be sent to journals, not for publication
but to certify priority of discovery.

At the same time Weisskopf also
cabled P.M.S. Blackett, a leading Brit-
ish physicist, asking whether it would
be possible for Nature and the Royal
Society’s Proceedings to cooperate in
delaying publication of fission research.
Meanwhile another of Szilard’s Hun-
garian physicist friends, Eugene Wig-
ner, wrote P.A.M. Dirac and asked him
to support Blackett. The matter was
rather urgent, Wigner said; although
American scientists were willing to co-
operate, they realized that their inter-
ests might be prejudiced if scientists in
other nations published results and
they did not.3’10 Blackett and another
prominent physicist, John Cockcroft,
promptly replied that they would sup-
port the secrecy plan. Nature and the
Royal Society were expected to cooper-
ate.3

Szilard, Teller, Weisskopf and Wig-
ner also talked the problem over with
Niels Bohr, who was visiting the United
States. Bohr doubted very much that
fission could be used to cause, a devas-
tating explosion. And he thought that
at any rate it would be difficult if not
impossible to keep truly important re-
sults secret from military experts — the
matter was already public. Neverthe-
less he agreed to go along with the at-
tempt and drafted a letter to his Insti-
tute in Denmark (which apparently he
did not immediately mail):

The Columbia group is busy orga-
nizing cooperation among all the
physics laboratories outside the dic-
tatorship countries, to keep possible
results from being used in a cata-
strophic way in a war situation, and I
must therefore ask you, if work along
these lines is going on in Copenhagen,
to wait before you publish anything
until you have cabled me about the
results and received an answer.11
But the conspirators still had to win the
agreement of other American laborato-
ries.

The most immediate problem was a
group headed by Richard Roberts work-

ing under Merle Tuve at the Carnegie
Institution in Washington, DC. They
too had recently seen some neutrons re-
leased from uranium. But the neutrons
they saw were emitted over a period of
some seconds after fission occurred:
These were not the true fission neu-
trons, but occasional neutrons produced
as a side effect of the radioactivity of
the fission fragments.12’13 The devel-
opment was announced in a news re-
lease of Science Service dated 24 Febru-
ary, written by Robert D. Potter, a
science writer who kept in touch with
the Columbia physicists and was infect-
ed with their_ excitement over chain re-
actions. Potter headlined the possibili-
ty of an explosive chain reaction propa-
gated by neutrons. He carefully noted
that Roberts’s delayed neutrons might
not be enough to sustain a chain reac-
tion— in fact they are not — but he quot-
ed Fermi as saying that the possibility
of a chain reaction was certainly
present.14

Szilard and his friends quickly ap-
proached the Washington group, who
promised to cooperate in withholding
future publications. The proposal was
spread further within the United States

SOCIAL CONTEXT

127

r

by word of mouth and letter. Maurice
Goldhaber of the University of Illinois
was included and Ernest Lawrence of
Berkeley was probably informed of the
matter when he visited New York on 3
April.15 John Tate, editor of the Phys-
ical Review, was brought in, for nearly
all important physics papers in the
United States passed through Tate’s of-
fice; anyone else who showed an interest
in fission neutrons could thus be put in
touch with the conspirators. The at-
tempt to restrict the circulation of in-
formation to physicists outside the dic-
tatorships was well begun. It lacked
chiefly the acquiescence of the French.

The French reply

The French knew what Weisskopfs
telegram implied, for they were as
alarmed as he by Hitler’s march
towards world war. However, like Bohr
and Fermi, the French believed an
atomic bomb was not likely to be built
for many years, if ever. In this they
were entirely correct, so far as atomic
bombs were then conceived — masses of
tons of natural uranium. Nobody had
yet seriously considered the likelihood
of isolating a substantial quantity of the
rare fissionable isotope U235, still less of
the undiscovered element plutonium;
and these two substances are the only

Iones that could in fact be used for a nu-
clear weapon. Unaware of these possi-
bilities, Joliot and his collaborators
thought that industrial nuclear power
from nuclear reactors was a much more
immediate prospect than weaponry.

It was up to Joliot, as head of the
team, to answer Weisskopfs telegram,
but he discussed it at length with his
colleagues. Thinking back, they re-
called a number of factors that entered
their decision.8’16 For one thing, Joliot
believed strongly in the international
fellowship of scientists, and in principle
had little sympathy with secrecy.17 For
another, if he and his colleagues failed
to publish, they might well be eclipsed
by those who did. For they could
scarcely believe that everyone would
adhere to an unprecedented pact, a pact
pushed forward, so far as they knew,
only by two Central European refugees
on the outskirts of the Columbia scien-
tific community. (Had Fermi, Bohr or
a leading American scientist written
them about the scheme, the French
might have found it more plausible.)
And if they failed to be first to publish
discoveries, the French might have
trouble getting the money they would
need to pursue the development of in-
dustrial nuclear energy. Finally, even
if all the laboratories joined and stuck
by the agreement, there would remain a
powerful objection, the same one noted
by Fermi and Bohr. It was scarcely
likely that copies of papers circulated
privately around America, France, Brit-
ain and Denmark could be kept out of

BREIT

Germany and the Soviet Union; more-
over, German and Soviet scientists were
surely aware of the importance of fis-
sion chain reactions.

Ideas of fission power and weapons
had begun to show up in the popular
press. The French were aware of at
least some of the sensational news
stories that emanated from the United
States. The French were not in close
touch with what was happening there,
but it is very likely that they had seen a
copy of a Science Service news release
of 16 March, which summarized their
own report, published in Nature on
that date, of neutrons resulting from
fission. Presumably they were not
pleased to read that they had apparent-
ly been beaten to the discovery: Their
result, the release said, “is comparable
with, and a confirmation of, the an-
nouncement (Science Service, 24 Febru-
ary 1939) that scientists at the Carnegie
Institution . . . had been able to observe
the same important reaction in atomic
transmutation.”18 This was an error,
but it made it seem that the most im-
portant facts were already leaking out
in America.

For all these reasons, the team cabled
Weisskopf a discouraging reply around
5 April.

SZILARD LETTER RECEIVED BUT
NOT PROMISED CABLE STOP PROPO-
SITION OF MARCH 31 VERY REASON-
ABLE BUT COMES TOO LATE STOP
LEARNED LAST WEEK THAT
SCIENCE SERVICE HAD INFORMED
AMERICAN PRESS FEBRUARY 24
ABOUT ROBERTS WORK STOP LET-
TER FOLLOWS

JOLIOT HALBAN KOWARSKI3

Szilard was well informed on the
work of Roberts’s group through their
publications and through letters from
Teller, who had visited them various
times, and on the next day, Weisskopf
having left New York, Szilard answered
on his behalf. Roberts’s paper, he
noted, concerned delayed neutron emis-
sion, which was harmless. But the
group had been approached and had
promised to cooperate. The American
group had delayed publishing papers;
were the French inclined to delay their
papers too, or did they think everything
should be published?

That same day the French sent their
final answer:

QUESTION STUDIED MY OPINION IS

TO PUBLISH NOW REGARDS JOLIOT.3

The scheme fails

This reply, along with the preceding
French publication of the fact that fis-
sion does produce some neutrons,
doomed the attempt to restrict publica-
tion. Pegram, who was not aware how
much progress Szilard and his friends
had made aside from the French, after
some days of deliberation decided that
any attempt to impose secrecy was
hopeless. Szilard was forced to give in.
The Columbia scientists asked the
Physical Review to print their papers.19

On April 7, the day of the final ex-
change of cables with Szilard, the
French sent Nature the results of ex-
periments and calculations that esti-
mated the number of neutrons emitted
per fission at between three and four.
The report was duly published on 22
April 1939. This note convinced many
physicists that uranium chain reactions
were a real possibility. In Britain,
George P. Thomson decided to warn his
government of the dangerous prospects
and meanwhile to begin experimenting
with uranium.20 In Germany, Georg
Joos wrote a letter to the Reich Minis-
try of Education; independently and si-
multaneously, Paul Harteck and Wil-
helm Groth wrote a joint letter to the
War Office.21 News of the French work
may also have played a role in the start-
up of Soviet nuclear energy research,
perhaps provoking the letters on urani-
um which I.V. Kurchatov and others
sent the Soviet Academy of Sciences
about this time.22 Thus in Britain,
Germany and perhaps the Soviet
Union, publication of the French results
precipitated offically-supported pro-
grams of research into nuclear energy.
The effort of Szilard and his friends,
after coming within an inch of success,
had failed disastrously.

Nevertheless, by the end of 1939 a
blanket of secrecy had settled over fis-
sion research in certain countries.
After war broke out in September, sci-
entists in France, Germany and Britain
withheld publication on fission and any

128

HISTORY OF PHYSICS

other subject remotely of military inter-
est. But in the United States, the So-
viet Union and other neutral countries,
publication was scarcely impeded.

US government: Do it yourself

Szilard continued to work on the
problem. With Albert Einstein he set
in motion a chain of events that led to
the formation of an official government
committee, under Lyman J. Briggs,
which was supposed to support and
coordinate fission work.23 From the
beginning Szilard hoped that the com-
mittee would also do something about
secrecy. When he took up the matter
with Briggs he added another element
to his by now increasingly well devel-
oped scheme. Presumably to counter
objections he had faced from younger
men at Columbia, he wrote:

For a physicist, who has not yet made
a name for himself, refraining from
publication means a sacrifice which
he should not be asked to make with-
out being offered some compensation.
Some addition to the salary which he
is normally drawing from the univer-
sity might therefore be desirable and
might require the creation of some
special fund.3

But the Briggs committee remained all
but inactive, leaving everything up to
the physicists. As late as 27 April 1940,
when the committee held one of its rare

meetings, the only response Szilard
could get was a suggestion from Admi-
ral Harold Bowen, present as an observ-
er, that the scientists working on urani-
um might get together and impose upon
themselves whatever censorship they
felt necessary. The government itself
would do nothing.3

Szilard had already taken the single
step that was entirely within his power:
He withheld from publication a paper
of his own. This paper, completed in
February 1940, contained elaborate cal-
culations of the characteristics of a nu-
clear reactor and concluded that there
was a strong possibility of making one
work. Had the article been published,
it surely would have been a great stimu-
lus to nuclear reactor work in various
countries. But when Szilard sent it to
the Physical Review he requested that
printing be delayed until further no-
tice.2 For a second specimen of a with-
held paper, in late April Szilard per-
suaded Herbert Anderson, a graduate
student who had worked closely with
Fermi on fission from the beginning, to
hold back his doctoral thesis on neutron
absorption in uranium, which was then
already in proof.24'25

Anderson and Fermi had meanwhile
been measuring the neutron-absorption
cross section of carbon: This difficult-
to-determine quantity was central to
the question of whether or not a nuclear

reactor could be built, for carbon
seemed the only feasible moderator,
and even carbon could be used only if it
absorbed virtually no neutrons. This
turned out to be the case: The cross
section was extremely small. Szilard
now approached Fermi and suggested
that the value for the cross section
should not be published. “At this
point,” Szilard recalled, “Fermi really
lost his temper; he really thought that
this was absurd.” But while Fermi
stuck by his principles, Pegram had sec-
ond thoughts and finally asked Fermi to
keep his work secret.1

This decision came late, but still in
time: If the value for the carbon cross
section had been published, the course
of World War II might conceivably have
been changed. For German scientists,
using experiments they carried out later
in 1940, wrongly concluded that carbon
had a substantial neutron-absorption
cross section. From that point on they
abandoned carbon as a moderator and
attempted to use the extremely rare iso-
tope deuterium, which they never man-
aged to get enough of.21’26 Soviet scien-
tists too at first did not seriously con-
sider carbon as a moderator.27 The
French scientists were also committed
to deuterium. They escaped to En-
gland when France fell to the Germans,
and thereafter the British followed
their lead in matters of reactors, regard-
ing carbon as an unlikely choice. An-
derson and Fermi’s work could have put
all these groups on a different track.

Prescription for a bomb

This was not the only hole in the dike
that had to be plugged. In late May,
Louis Turner at Princeton sent Szilard
a copy of a paper on “Atomic Energy
from U238.” In this paper Turner
pointed out that if U238 were bombard-
ed by neutrons, as would happen in a
nuclear reactor, a series of steps would
give rise to a new element. This he pre-
dicted to be fissionable — it was the ele-
ment later named plutonium. Al-
though Turner had not realized it, he
had written the prescription for the eas-
iest route to building an atomic bomb.

Szilard wrote back at once to say that
his own paper was secret, implying that
there was an official move underway to
withhold papers. He persuaded Turner
to write the Physical Review and delay
publication.3 It was well he did so:
Turner’s paper could have been an es-
sential clue for the Germans and others.
Meanwhile Szilard approached Harold
Urey and asked him to try to set up a
committee to regulate fission publica-
tions.

Before much progress had been
made, the 15 June issue of the Physical
Review appeared, containing a letter
from Edwin McMillan and Philip Abel-
son at Berkeley. They had observed
the production of neptunium when ura-

Exploding Uranium Atoms
May Set Off Others in Chain

Explanation Suggested at Physics Meeting Believed
By Prof. Fermi To Be One of Several Possibilities

'XPLODING atoms of uranium may hit another uranium atom
' each other off in a chain like too.
ck ' laid in a row. New

stick

am

cr ■ nu m i

post 't’c'£.vcf y '-’vc rup-
ture "i ,

of ’ °r ■1Pr'l /,

the ^J"u
th<
it
A

too.

work on uranium sp
that lor a single net

Prior u,

indicated that lor a .ungie nc
a single uranium atom

'nt Hut it mac

. ~’°n'irrn /?„/

f'°m Sri«tsUrtNeUt

w cGnfi 9 Uranium A

hrannim <%fCover,, ,onhr;nC(j , %€»I|

Two history-making releases from Science Service, as reprinted in Science News Letter.
After reading an erroneous statement in the later (lower) article, which said that their results
had already been published in America, the French team rejected Szilard's request for secrecy.

-

SOCIAL CONTEXT

129

nium was bombarded with neutrons.
This was the first and most essential
step of the process that Turner had pre-
dicted should lead to plutonium. But
Abelson and McMillan had simply
failed to see the connection between
their work on transuranic elements and
the fission problem.15,28

This publication brought down a flur-
ry of protest, which helped to settle the
secrecy issue. From as far as Britain,
scientists interested in fission protested
the publication of such revealing infor-
mation. But the most important news
came from Gregory Breit at the Univer-
sity of Wisconsin. Breit had known
Szilard and Wigner for years, and was
awakened to the secrecy problem
through long conversations with them.
Around the beginning of June Breit
found a way to circumvent the prob-
lems Szilard and others were running
into. Recently named to the National
Academy of Sciences, he had been put
in the Division of Physical Sciences of
the Academy’s National Research
Council. At a committee meeting he
spoke up in favor of censorship. There
was some skepticism, Breit later re-
called, but a committee on publications
was appointed to consider the problem.
Breit was made chairman of a subcom-
mittee concerned specifically with ura-
nium. Acting on his own initiative, he
immediately began writing letters to
journal editors, proposing a voluntary
plan under which papers relating to fis-
sion would be submitted to his commit-
tee before publication. Sensitive pa-
pers would be circulated only to a limit-
ed number of workers. Breit added
that he expected ultimately to publish
the papers in book form or otherwise,
with a statement of the original date of
the paper and with a suitable acknowl-
edgment of the public spirit of the au-
thors.15

There were some raised eyebrows,
but the editors of scientific journals and
other leading scientists agreed to the
plan. “As recently as six months ago,”
Lawrence wrote Breit, “I should have
been opposed to any such procedure,
but I feel now that we are in many re-
spects essentially on a war basis.”15
German troops were pursuing the rem-
nants of the defeated French army, and
none could doubt that the international
situation was desperate.

Better than never

Within a few weeks Breit, who swiftly
set up close communications with
Fermi, Urey, Wigner and others in-
volved in parallel efforts at secrecy, had
imposed total censorship on American
fission research. After passing the pa-
pers around by mail for comment,
Breit’s committee let some through as
innocuous; other they withheld from
publication.25 Because of this proce-
dure, carried out entirely by physicists

with no government participation, long
before the United States went to war it
was keeping vital scientific information
within its own borders.

The extraordinary coincidence that
history’s most dangerous scientific se-
cret appeared at the moment history’s
greatest war began made possible this
unique case of scientific self-censorship.
It was imposed against the grain — even
some of the conspirators, like Szilard
and Teller, would later argue strongly
for the advantages of open publication.
But it is worth noting that if self-cen-
sorship is difficult, under sufficiently
deadly circumstances it can be
achieved, and that if it may seem to
come late, late may be far better than
never.

* * *

I wish to thank first of all Gertrud Weiss Szi-
lard, who kindly gave me permission to use
the Szilard Papers and topublish theexcerpts
above. Thanks are also due to Helene Lange-
vin, who kindly made available the Joliot-
Curie Papers; to Monique Bordry, who gave
invaluable assistance in their use; to Gregory
Breit, Otto Frisch, Victor Weisskopf and par-
ticularly Lew Kowarski, who answered the
questions I posed them, and to Charles
Weiner, who assembled interviews and other
materials at the Center for History of Physics
of the American Institute of Physics. For
further details see Weart and G. W. Szilard,
eds., Leo Szilard: His Version of the Facts,
MIT Press, Cambridge (1978); Weart, Scien-
tists in Power, Harvard University Press,
Cambridge, (1979). All translations are my
own except for the Bohr letter, for assistance
with which (and for much else) I thank John
Heilbron.

References

1. L. Szilard, “Reminiscences,” The Intellectual
Migration, Europe and America, 1930-1960
(D. Fleming and B. Bailyn, eds.) Harvard
U.P., Cambridge, Mass. A revised and ex-
panded version is in Leo Szilard: His Version
of The Facts (see note above).

2. The Collected Works of Leo Szilard,
Volume 1, Scientific Papers (B. T. Feld,
G. W. Szilard, eds.), MIT Press, Cam-
bridge, Mass. (1972).

3. Szilard papers, La Jolla, Calif.

4. Bainbridge collection, American Insti-
tute of Physics, New York.

5. J. D. Bernal, The Social Function of
Science, Routledge & Kegan Paul, Lon-
don (1939), pages 150, 182.

6. Pegram collection, Columbia Univ. Li-
brary.

7. Joliot-Curie papers, Radium Institute,
Paris.

8. Testimony of L. Kowarski before the US
Atomic Energy Commission’s Patent
Compensation Board, Docket 18, 16
March 1967, Energy Research and De-
velopment Administration, German-
town, Md.

9. H. von Halban, F. Joliot, L. Kowarski,
Nature 143, 470 (1939); The Discovery of
Nuclear Fission: A Documentary His-

tory (H. Graetzer, L. Anderson, eds.),
Van Nostrand Reinhold, N. Y. (1971).

10. Copies are in ref. 3; the original is in
Dirac papers, Churchill College, Cam-
bridge, UK.

11. Bohr Scientific Correspondence (copies
are held at the American Institute of
Physics, New York; American Philo-
sophical Society Library, Philadelphia;
Bancroft Library, Berkeley, and Niels
Bohr Institute, Copenhagen).

12. R. B. Roberts, R. C. Meyer, P. Wang,
Phys. Rev. 55,510(1939).

13. R. Roberts, L. R. Hafsted, R. C. Meyer,
P. Wang, Phys. Rev. 55, 664 (1939).

14. Science Service, 24 Feb. 1939; reprinted
in Science News Letter, 11 March 1939,
page 140.

15. Lawrence papers, Bancroft Library,
Berkeley, Calif.

16. R. Clark, The Birth of the Bomb: The
Untold Story of Britain's Part in the
Weapon that Changed the World, Hori-
zon, New York (1961); B. Goldschmidt,
Les Rivalites Atomiques 1939-1966,
Fayard, Paris (1967), page 27; interview
of Kowarski by Weiner, American Insti-
tute of Physics.

17. F. Joliot-Curie, Textes Choisis, Editions
sociales, Paris (1959), page 154.

18. Science Service, 16 March 1939; reprint-
ed in Science News Letter, 1 April 1939,
page 196.

19. R. B. Anderson, E. Fermi, H. B. Han-
stein, Phys. Rev. 55, 797 (1939); L. Szil-
ard, W. H. Zinn, Phys. Rev. 55, 799
(1939).

20. M. Gowing, Britain and Atomic Energy,
1939-1945, St. Martin’s Press, New York
(1964), page 34.

21. D. Irving, The Virus House: Germany’s
Atomic Research and Allied Counter-
Measures, William Kimber, London
(1967), page 32.

22. I. N. Golovin, I. V. Kurchatov: A Soci-
alist-Realist Biography of the Soviet
Nuclear Scientist (H. Dougherty,
transl.), Selbstverlag Press, Blooming;
ton, Ind. (1968), page 31.

23. R. G. Hewlett, O. E. Anderson Jr, The
New World: A History of the United
States Atomic Energy Commission, vol-
ume 1: 1939-1946, Pennsylvania State
U. P., University Park, Pa. (1962), page
16; Briggs Committee correspondence,
Atomic Energy Papers, Office of Scien-
tific Research and Development, Nation-
al Archives, Washington, DC.

24. E. Fermi, Collected Papers, volume 2:
United States 1939-1954, (E. Segre et
al, eds.) University of Chicago Press,
Chicago (1965), page 31.

25. Samuel A. Goudsmit collection, Library
of Congress, Washington, DC.

26. W. Bothe, P. Jensen, “Die Absorption
thermischer Neutronen in Elektrograph-
it,” 20 Jan. 1941, captured German re-
port G-71, Technical Information Ser-
vice.

27. Bulletin de l’Academie des Sciences de
l’URSS, Ser. Phys. 5, 555 (1941); a trans-
lation by E. Rabinowitch, Report CP-
3021, is available from Technical Infor-
mation Service, Oak Ridge, Tenn.

'28. E. McMillan, P. H. Abelson, Phys. Rev.
57, 1185 (1940). □

.

130

HISTORY OF PHYSICS

By E. V. Condon

PHYSICS TODAY / APRIL 1952

The following is an address given by Dr.
Condon on September 25, 1951, less than
one week before his resignation as direc-
tor of the National Bureau of Standards
became effective. His talk was prepared
for delivery at the National Academy of
Sciences in Washington.

\ S MY NEARLY SIX YEARS of service as Di-
■C*- rector of the National Bureau of Standards draw
to a close, it seems that an important final part of that
service would be to set down some over-all views con-
cerning the scientific work of the Federal Government
growing out of that experience. Our governmental insti-
tutions are so close to us that I had some experience
with them before entering Federal service full-time, es-
pecially during World War II, and likewise I expect to
have association with such matters in the future while
in private employment.

It seems to me that the scientific research activities
of the Government are on the whole good but never-
theless, like all things human, capable of improvement,
and it is to some suggestions for improvement that I
will principally turn my attention.

The first general point I wish to make is the very
obvious fact that the whole complex of modern ma-
terial civilization arises from application of scientific
knowledge. All modern engineering and industry, agri-
culture and medicine is based on the results obtained by
consciously planned laboratory experimentation within
the last three centuries, and largely within the last cen-
tury. It is this new type of activity which has in the
last century made greater changes in our material ways
of life than have occurred in thousands of years before.
The improvement of the conditions of life through the

£

lightening of burdens by the development of mechanical
power from flowing water and from fuels, the improve-
ment of our homes and clothing by modern products of
applied science, the more effective production of foods
and the use of refrigeration for their large-scale preser-
vation and wide distribution, the increased knowledge
of nutritional principles, the improvement in all kinds
of techniques of medicine and surgery — all these may
be counted as great blessings to mankind resulting from
the cultivation of science and its application to our ma-
terial needs.

Even greater perhaps than all those material bene-
fits, however, is the benefit that comes from the free-
ing of men’s minds and spirits from the oppressiveness
of superstitious belief and the growing realization that
we live in a world of law and order that is intelligible
to us if we will but discipline ourselves to the effort
necessary to understand its structure and workings.
Certainly this spiritual blessing, in common with the
material blessings already mentioned, should combine
to produce in all of us the recognition that scientific
study is one of the most rewarding fields of human en-
deavor possible in the world today.

Science is a method by which we learn to know in
ever wider ways and with ever greater precision about
the world in which we live. The study of science can
make genuine and wholesome contributions to char-

Ewing Galloway photo

acter development not the least of which is an uncom-
promising demand for truth and honesty in all the af-
fairs of life and a proper humility before all the many
winders which surround us. But great as I think are
the values which science has brought and will bring to
humanity, I would not wish to leave you with the im-
pression that man can live by science alone, for science
does not provide him with the ethical guidance nor the
spiritual insights which are needed to realize our ideal
of the good life.

Not all of the consequences of this enormous in-
crease in man’s knowledge of the world have been bene-
ficial nor can it be said that wre are effective in making
the fullest use of the knowdedge we already have. We
have been slow to bring about a widespread distribu-
tion of these benefits to all of the population of even
a wealthy and favored nation like the United States.
While steady progress is being made — at a lamentably
slow pace — the fact is that we have done very little
toward slum clearance in our major cities or toward
providing adequate schools and hospital service for all
of the population. We are doing very little to assist the
underdeveloped countries to bring the benefits of mod-
ern applied science to improve the welfare of the hun-
dreds of millions of their population.

We talk of bold new programs in this direction, and
we feel uneasily that much more needs doing than we

have undertaken so far, and still we do essentially
nothing about it. Our carelessness here is storing up
great trouble for us in the future. We in America and
in Western Europe are a small minority among the
world’s peoples. Other hundreds of millions of persons,
chiefly in Asia, have caught a glimpse of what modern
science can do for them and they are determined to
have it. If we help them we can have their friendship
as equals. If we do not, they will get these benefits for
themselves anyway in the course of time, and on terms
which will involve a great deal of strife and difficulty
for us. It is true we have done much to assist in the
reconstruction of Western Europe, but we have done
practically nothing to assist the development of Asia
and Africa. We have not even made effective plans for
relief and reconstruction in the devastated areas of
Korea.

The effort in this direction that I feel is necessary
will be very great but it is my sincere conviction that
effort of this kind is the most important thing we can
do to preserve and extend the kind of Christian demo-
cratic civilization which we believe in. I believe that
this kind of constructive effort to assist in bringing the

E. U. Condon is director of research and development for the Corning
Glass Works, Corning, N. Y. He was director of the National Bureau
of Standards from 1945 to 1951. He has been scientific advisor to the
Special Committee on Atomic Energy of the U. S. Senate since 1945.

HISTORY OF PHYSICS

benefits of modern science to the whole world is the
only kind of effort which will accomplish the construc-
tion of the kind of world in which peace and goodwill
can reign. I do not regard this required effort as a
burden but as a great opportunity which has been pre-
sented to us which we should be grasping with eager-
ness and enthusiasm.

While it may be necessary, under present conditions,
to use our scientific knowledge and our industrial pro-
ductive capacity largely for building up our military
strength, I am convinced that we are, perhaps uncon-
sciously, placing too great an emphasis on this, as if it
would give us the means of solving the difficult social
problems with which we are confronted. All that we can
hope for from military strength is that it will enable us
to preserve a situation in which Western civilization
will have an opportunity to share its wealth-producing
techniques with the other peoples of the world, instead
of having them snatched from us by angry hordes of
men who outnumber us ten to one and who will have
come to resent bitterly the seeming hypocrisy of our
attitudes toward them. I will not therefore go so far as
to say that under present conditions the building up of
military power on which we are again engaged is now
avoidable. But this course of action by itself may prove
fruitless unless it is accompanied by a very great pro-
gram— one whose scale of effort is at least as great as
that we are putting into building up our armaments—
that is designed to help all peoples of the world who
are willing to work with us, to achieve the benefits of
modern science which we enjoy. If we do this we shall
derive great spiritual benefit from the increased happi-
ness of these millions of God’s people and material
benefits from our participation in the contributions
which their intelligence can bring to our unsolved
problems.

'"pHERE IS ANOTHER ASPECT of recent tend-
encies in development of military armament which
we need to consider very carefully. War at best is an
evil thing in which peoples resort to force to impose
their will on each other instead of using love and com-
passionate efforts at mutual understanding to arrive at
a solution of their difficulties. The opening years of this
century were marked by all kinds of efforts in the way
of agreements for the humanitarian treatment of pris-
oners, in agreements to confine the fighting to organ-
ized military forces, and even in agreements to avoid
the use of certain particularly horrible weapons such
as dum-dum bullets. In the two world wars of recent
years, and in the military rearmament which is now-
going on, such ideas have become quaintly old-fashioned.

No longer do we give the slightest consideration to
the distinction between military and civilian popula-
tions. In World War II both sides gave very little re-
gard to avoiding destruction of the civilian population
of their enemies, and enormous damage was done to
other than strictly military objectives. A minute part
of this terrible destruction was made by the use of the
bombs based on the fast neutron fission of uranium and

plutonium. The loss of life in Japan alone due to fire
raids using napalm was much greater than that due to
atomic bombs.

A large part of our organized effort in modern sci-
ence goes today into putting enormous teams of men to
work on developing even more deadly and destructive
weapons than the world has ever seen before. We talk
openly of germ warfare and nerve gases and we almost
never hear of these being criticized as inhumane and
revolting to the consciences of Christian men and
women. No, we hear them criticized because it is diffi-
cult to produce germ cultures or gases in sufficient
quantity or concentration to wipe out the -whole popu-
lation of a city as their proponents would say is pos-
sible and therefore we should devote our attention to
the creation of some other fiendish thing like the hy-
drogen bomb. This, in turn, we hear criticized, not in
terms of revulsion that men would use such things
against each other, but that maybe its destructiveness
is too concentrated and that the same effort put on
more conventional types of atomic bombs would en-
able destruction to be carried out over an even greater
area.

At San Francisco a few weeks ago the President
spoke unspecifically of fantastic new weapons too hor-
rible even to describe. The press was thereby filled with
all kinds of science fiction speculations about what
these horrible new wonders might be. Within a few
days Congress increased the already enormous appro-
priations to the Air Force by five billions. In a matter
of hours the Congress gave five billion for fantastic new
weapons of which it knows next to nothing — the same
Congress which after long debates finally cut one bil-
lion dollars out of the foreign aid program, the same
Congress which by its long delays did much to nullify
the effects in promoting goodwill of our finally supply-
ing a credit (not a gift) for $190 million for grain to
alleviate severe famine in India; the same Congress
which refuses to provide $300 million in Federal aid to
our overcrowded and inadequate school system, the
same Congress which has lopped off the paltry appro-
priation of $14 million for the National Science Foun-
dation which was intended to give some slight nourish-
ment and sustenance to the fundamental scientific re-
search on which rests the whole structure of modern
industry, agriculture, and medicine.

Some may think that in referring to $14 million for
the National Science Foundation as a paltry sum I
speak like one of those terrible bureaucrats who has no
regard for the burdens which the taxpayer must bear.

I am concerned about taxes but I also want us to show
some sense of proportion. Congress is this year spend-
ing $60 billion of new money or a total of about $100
billion of available funds on the Department of De-
fense. It has just increased this by another $5 billion
for “fantastic” new weapons which the newspapers say
can “conquer the atmosphere,” whatever that means.
It is spending $6 billion on foreign aid much of which
is for rearmament rather than economic development.

Included in the military appropriations is about $1.5

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133

billion for military research and development, a stag-
gering sum of money which, if invested at 6% interest,
would produce annually as much money as Congress
has appropriated to the National Bureau of Standards
in the entire fifty years of its existence. But it cannot
spare $14 million next year for strengthening basic
scientific research.

Today every activity of Government is being ad-
judged solely on the basis of its contribution to de-
fense. I doubt whether such vast sums can be spent
w'isely for the purpose intended, and whether it is wise
to put so much of our reliance on military strength
while thinking so little about peaceful and constructive
solutions of the difficult domestic and international
problems before us.

If so much of our scientific effort is directed toward
military weapon development, it must necessarily mean
neglect of the basic science on which future progress
must be built and neglect of the application of modern
science to improving human well-being in our own and
other parts of the world. There is another reason why
we might be disturbed at the extent to which science is
devoted to military purposes today. Although it seems
to be very little in evidence at the moment I believe
that deep in the consciences of men and women there
is a horror and revulsion at the terrible means and
methods of modern warfare which will some day find
expression in a new and powerful and constructive de-
termination to live together peacefully, and effectively
to renounce war as an instrument of national policy.
If in the years to come science and the scientists are
closely identified in the public minds as the wizardry
and the wizards who have made all the fantastic new
weapons of mass destruction that Governments are
now so eagerly urging them to produce, this horror and
revulsion of war may, in that illogical and irrational
way that so many things go in politics, be extended to
science and the scientists. If this were to happen it
would be bad not only for the scientists, but it would
be bad for society, for a rejection by society of the
method and power of scientific inquiry will stop prog-
ress in understanding and tend to retard the extension
to all mankind of its beneficial applications. If men’s
consciences reawaken to the absolute necessity of abol-
ishing warfare, then there may be serious danger that
science may be the baby which is thrown out with the
bloody bath which is War.

This situation poses very difficult problems for scien-
tists in general and especially for those in official po-
sitions in our Government. Speaking personally, all of
my friends know with what strong conviction I hold
the general views which I have tried here, rather in-
adequately I am afraid, to outline. When I came to
Government service at the close of World War II, I
hoped and believed that there was to be an era of
peace in which fundamental research in science would
flourish and be supported by society as a whole as a
worthy intellectual activity and for the constructive
benefits to man’s well-being which it can bring. At that
time, only six years ago, the United Nations had just

been born and many of us believed that the experience
of wartime alliance had taught the lessons which would
gradually enable the growth of a mutual confidence
and trust between Russia and the United States and
other principal nations of the world which would re-
move any basis for future war of major proportions.
In such a setting one could hope for a steady reduc-
tion of national armaments, with the enormous eco-
nomic waste which they imply, and their replacement
by an international police force. In such a setting we
hoped that all efforts in the field of atomic energy
would go to peaceful purposes in chemical and medical
research and in making available new sources of power.

At this time it seemed that Congress and the people
of the United States, impressed by the contributions
which applied science had made during the war, were
prepared to support a National Science Foundation in
a really adequate way — by this I mean to the extent of
several hundred million dollars a year — and that science
in other countries would be aided by a major program
of the United Nations Educational Scientific and Cul-
tural Organization as well as by local efforts in those
countries.

During my first year in Washington, 1945-46, my
attention was largely taken up with assisting the Spe-
cial Senate Committee on Atomic Energy of the 79th
Congress, as scientific adviser, when it was developing
the Atomic Energy Act of 1946 by which the present
Atomic Energy Commission was established.

During that first year the Senate held extensive hear-
ings on proposed legislation for the National Science
Foundation and passed a bill, but this was allowed to
die in the House when the situation became confused
by behind-the-scenes lobbying of those who insisted on
a large part-time board for the Foundation. Otherwise
the National Science Foundation probably would have
started operating five years ago with an annual appro-
priation of about two hundred million dollars. If this
had been allowed to happen we would have been in-
comparably better off than we are today from every
point of view. Fortunately, the vacuum thus left was
quite well filled by the enlightened scientific research
program of the Office of Naval Research. This was con-
ducted as liberally and as intelligently as any purely
civilian program could possibly have been conducted
and has made a wonderful contribution to the develop-
ment of basic science in America during the post-war
period.

COON AFTER THAT FIRST post-war year it be-
came clear that expenditures for scientific research
for military purposes would be maintained at a high
level and expanded above the minimum reached in the
demobilization period. Work in this field has always
been an important part of the program of the labora-
tories of the National Bureau of Standards. The Bu-
reau has a long history in meeting such military needs,
having first developed the optical glass industry in
World War I, having initiated the atomic bomb project
in World War II, and also having played a large part

HISTORY OF PHYSICS

in the development of proximity fuzes, having devel-
oped the only fully automatic guided missile to be used
in warfare thus far, and having done much to improve
knowledge of long-distance radio transmission on which
the continuity of military communications depends.
This latter service was initiated during World War II
and organized as a permanent service in the Bureau
during the first post-war year. Congress has been will-
ing to support this work reasonably well and has made
provision for splendid new laboratories for the radio
work of the Bureau to be built in Boulder, Colorado.
This radio work is, however, essentially the only new
activity of the Bureau for which it has been possible
to get direct financial support from the Congress dur-
ing the post-war years.

In this period, to be sure, and particularly during the
last year, there has been a great expansion in the level
of activity of the Bureau. But this has not been by di-
rect Congressional support, but rather by doing project
work in Bureau laboratories for the armed services and
with funds provided by them from their own appro-
priations. For example, this fiscal year the Bureau will
operate on a total budget of some 60 million dollars,
less than $10 million of which is directly appropriated
by the Congress, nearly all of the rest being paid by
the military for work done for them. To get some idea
of the disparity of figures involved it is interesting to
note that this year the Bureau will spend on electronic
ordnance developments alone about 50% more money
than the $14 million which the House has refused to
give the National Science Foundation for Federal sup-
port of basic science.

The amount of military work done by the National
Bureau of Standards has increased almost by a factor
of seven during the time that I have been Director.
Provision has been made for expanded facilities for
such work in Washington, in Boulder, Colorado, where
large new Bureau-operated laboratories are being built
for work of the Atomic Energy Commission, and also
in Corona, California where some unused former Naval
hospital facilities have been converted into a splendidly
equipped development laboratory for guided missile
work for the Navy. Another Bureau development of
military importance has been the establishment of a
department of applied mathematics with facilities both
in Washington and Los Angeles, and the development
of an important electronic digital computer, the SEAC,
which has been in service for more than a year on mili-
tary problems. These are just highlights of a program
which involves dozens of research projects of specifi-
cally military interest some of which relate directly to
fantastic new weapons which cannot even be men-
tioned. I think therefore that the National Bureau of
Standards is in a stronger position than ever before to
make important contributions to military needs.

Turning to the fundamental support of the civilian
program of the Bureau the situation is far from satis-
factory. The National Bureau of Standards is a Cinder-
ella whose Prince Charming has yet to come along. In
spite of its long record of splendid accomplishments, its

scientific program was crippled by severe budget cuts
in 1933 as one of the economy acts of the Roosevelt
administration. Valiant efforts were made by my prede-
cessor, Dr. Briggs, to hold an effective staff together in
spite of this short-sighted action but the Bureau is
still suffering from the effects of that decision.

Except for the expanded radio work the direct sup-
port available for the Bureau in the post-war years has
remained nearly constant, as expressed in dollars, and
therefore has declined steadily in real purchasing power
for goods and materials. This is a most serious situa-
tion, for it has occurred at a time when there has been
a steady growth in the amount and complexity of the
needs for standards of precise physical measurement.

Every kind of physical quantity is being measured, in
connection both with scientific research and with more
accurate control of industrial processes, with greater
precision than before, and over a wider range of ex-
treme conditions, and the need for exact calibrations of
measuring instruments arises from a much greater num-
ber of research laboratories and industries than ever
before. This has put a burden of work on the National
Bureau of Standards with which it is quite unable to
cope within the framework of its present appropria-
tions. Try as we will we have not been able to keep
up with the demands for such services. The result is,
of course, that much money is wasted by others in
duplications of calibrating set-ups which the Bureau
should have and that many scientific jobs are done with
a lower grade of accuracy than desirable and than
would be possible if the National Bureau of Standards
were allowed to render an adequate service.

I confess that I do not know how to do a better job
of bringing this need to the attention of the Govern-
ment. It has received a great deal of my attention in
the last five years but with essentially no results. I
hope that my successor in office will be able to do
better on this than I have. Here it is important for him
to realize that not all of the difficulty is with Congress.
The budget of the National Bureau of Standards has to
pass four hurdles before it is approved. It must first be
approved by the budget officers of the Department of
Commerce. It comes before them as a peculiarly diffi-
cult-to-understand technical item which amounts to less
than two per cent of the total budget requirements of
that Department. Since it is such a small part of
the Departmental budget it is only natural that these
budget officers have no scientific and technical back-
ground. At this stage efforts to get even what increase
is necessary to keep abreast of the declining purchas-
ing power of the dollar are pretty well nullified because
these men are working under a general over-all limita-
tion as to what the Department of Commerce itself
may have.

After the Department of Commerce has finished its
consideration, the Director and his staff must write up
the whole thing again in great and specific fiscal detail
for the Bureau of the Budget. This is supposed to show
that the whole program of proposed work has been very
thoughtfully considered. Having filed all this data with

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135

the Bureau of the Budget, several hours are spent ex-
plaining the needs to staff officers of the Bureau of the
Budget. Here again because scientific research is dif-
fused over the whole structure of the government one
is dealing with individuals who have very little back-
ground either in the over-all needs of the Government
for scientific research, or in the accomplishments of the
National Bureau of Standards in particular, or for the
methods and aims of physical science in general.

This process goes on intermittently during the first
half of the fiscal year preceding the one for which the
budget is being prepared. Out of it comes an official de-
termination by the Bureau of the Budget of what each
governmental agency will be allowed to ask for in going
before the Appropriations Committees of the House
and Senate. The end result of this process when car-
ried out for all the agencies of the Government ap-
pears in a large document which is printed and trans-
mitted to Congress as the President’s Budget. This is
now official, and sometime in the spring the Director
and his staff are summoned down to present the Bu-
reau’s part in the President’s Budget to his subcom-
mittee of the House Appropriations Committee and
then to the Senate Appropriations Committee. Before
doing this, however, his own staff of budget officers
have had to rework completely the elaborate document
by which the plans for the coming fiscal year were
submitted to the Bureau of the Budget.

It is hard to convey any idea to persons outside of
the Government of the extent to which the working
agencies are called on to supply over and over again
statistical reports about their work which cover essen-
tially the same ground in slightly different forms.

Each agency sends up a large budget document to
the Congress for the use of the Appropriations Com-
mittee in advance of the hearings. At the hearings the
questioning often indicates that the Congressmen have
very little understanding of the particular scientific
needs of a technical agency and that perhaps they have
not had time to look at the contents of the elaborate
budget document which was prepared for them.

SOME OF MY most treasured memories of Govern-
ment service are connected with incidents which oc-
curred in these appropriations hearings. One feels rather
nervous and tense on these occasions for on their out-
come hinges the whole fate of the Bureau’s work.

One time while waiting our turn outside the com-
mittee room, the budget officer of the Patent Office
came out of the door looking pale and fell on the floor
of the hall in a dead faint. We bustled around adminis-
tering first-aid and when he came to partially he mut-
tered deliriously, “It’s awfully hot in there.” Later,
when it was my turn to go in, I found that he was
right. That was during the Eightieth Congress at a
time when the Alsops referred to the House Appro-
priations committee as a bunch of blind men pruning
a jungle.

I remember one time one Congressman had me quite
upset because he was scowling through the whole of

my presentation. When it came his turn to ask ques-
tions he asked me, “Doctor, where is the National Bu-
reau of Standards?” I told him it was out on Con-
necticut Avenue and he said excitedly, “Is that what
that place is?” and became quite friendly.

On another occasion a Congressman was questioning
the chief of the Bureau’s radio division, who had been
talking about the scarcity of space in the radio fre-
quency spectrum for the many needs of communica-
tion services. He said: “Doctor, I understand that
among you scientists there are two theories: some say
space is finite, others say it is infinite. I want to know,
where do you stand?” The witness started to explain
the limitations of using very low and very high fre-
quencies but the Congressman interrupted him to say,
“No, I mean space, you know, space,” making a large
and globular gesture toward the part of the three-di-
mensional continuum in front of him.

The witness squirmed and looked at me for guidance,
quite willing to make it finite or infinite for the sake of
the budget, but I could only indicate with a gesture that
I did not know which was the preference of that par-
ticular Congressman. So he gulped hard and said, “I
think it’s infinite.” “Thank you very much, Doctor,
that’s all I wanted to know”, replied the Congressman
and passed on to another topic.

When these hearings deal with science they are apt
to be rich in non sequiturs. For example, only yester-
day I was reading the Senate defense appropriation
hearings (p. 1177) where an Army colonel is asking for
funds for an electronic computer for logistic planning.
A Senator asks him: “Now, is there any relationship
between the number of equations that have to be de-
veloped and the time the machine is in operation?”
And the colonel replies: “Electricity travels 186,000
miles per second, sir, so it is an infinitesimal difference.”

There would be no point in describing this procedure
in such detail unless I had a suggestion to offer. I do
have.

I am convinced that the over-all importance of scien-
tific research in Government has become so great that
it requires careful attention and study by a new stand-
ing committee of the Congress. It is at least as impor-
tant as atomic energy which has a permanent Joint
Committee, affording an organized means by which
Congress can study these problems. A similar means
is needed for scientific research broadly if we are to
get intelligent action and focus attention on unwise ac-
tions or inactions. Such a committee would study and
deal with legislative problems affecting scientific research.

In addition it would be very desirable if the Appro-
priations Committee of the Congress would find a
formal way to give some unified over-all attention to
the scientific research requirements of the Government.
A legislative committee on science in the Congress
would not be enough unless the Appropriations Com-
mittees were also prepared to have a look at the whole
program of all the large variety of specialized agencies
in the government which are doing scientific work.

The most natural way for the Congress to deal with

HISTORY OF PHYSICS

science in a unified way would be for the scientific
agencies of Government to be gathered up into what
would be in effect a single Department of Government.
I believe that the general importance of scientific re-
search in the Federal Government has become so great
that this should be done. If it were not considered de-
sirable to establish a new Department of Scientific Re-
search then I would recommend that the Smithsonian
Institution be used for this purpose. I believe that the
new Department or enlarged Smithsonian Institution
should include all of the scientific agencies of Govern-
ment including the major military research laboratories,
the research laboratories of the Atomic Energy Com-
mission, the National Bureau of Standards, the Na-
tional Institutes of Health, the laboratories of the De-
partment of Agriculture, the Weather Bureau, and the
Bureau of Mines, the Geological Survey, the National
Advisory Committee for Aeronautics, and, of course,
the National Science Foundation.

Whether a new Department of Scientific Research in
the Executive Branch or an enlarged assignment of re-
sponsibilities for the Smithsonian Institution represents
the better proposal I am not prepared to say. But it
seems clear to me that a unified administration of the
scientific affairs of the Government, including unified
treatment of them by the Bureau of the Budget and
by appropriations and legislative committees of Con-
gress, would surely be an improvement over the present
situation. I am inclined to favor the adaptation of the
Smithsonian for this purpose over the creation of a
new Department, for the reason that each cabinet
member is on the board of the Smithsonian and thereby
the relation of science activities to the other govern-
ment activities they support would be preserved while
giving scientific research as a whole a coordinated ad-
ministration.

The suggestion that the Bureau of the Budget should
have a special staff for study of the needs of scientific
research is not a new one, having been made as a rec-
ommendation in the Steelman report, entitled “Science
and Public Policy.” But it has never been acted upon,
I suppose, because of the difficulty of finding properly
qualified individuals to do the job and the Budget Bu-
reau may feel that it is better to do it not at all than
to do it badly.

If there is any merit in the general suggestions I am
making I would like to see the Bureau of the Budget
call on the National Academy of Sciences for a study
and recommendations and also to ask the Academy for
its help in reviewing the budget of the existing agen-
cies. The Congress too should recognize the many ways
in which it could get help on scientific problems from
the Academy and call on it for help more often on
large broad issues than it has in the past.

As part of such a plan, the National Academy of Sci-
ences, the National Research Council, the American
Association for the Advancement of Science, and the
specialized scientific societies would retain the inde-
pendent status which they have now but would work
in close cooperation with the new science administra-

tion to make sure that the Government’s research pro-
gram is effectively carried out in a way best suited to
serve the national interest in relation to the profes-
sional needs of the scientific work in the universities
and in industry.

/"\NE OF THE MOST REMARKABLE omissions
in the report of the Hoover Commission on the
reorganization of the Government was its almost com-
plete lack of any recommendations for improving scien-
tific research in the Government. This is hard to un-
derstand for surely the men who developed that report
appreciate the importance of science today in Govern-
ment, and cannot have felt that the present diffusion
of responsibility over many separate agencies is a form
of organization which cannot be improved upon.

It seems to me all the more important that a unified
central body for science in Government be set up be-
cause research is a very fashionable thing these days
and every new agency feels it must do research in order
to have status in the world of bureaucracy. While it is
very difficult to get adequate support for the established
research agencies, it is always possible to set up a re-
search program as a small part of a general need to
which assent has been given and by indirection to ob-
tain vaster sums of money than the established agen-
cies can get for research. For example, it would be ex-
tremely difficult the way things are now to get a modest
increase in the funds available to the National Bureau
of Standards for research on synthetic rubber in spite
of a splendid record of past achievement, whereas a
quite substantial amount of support is carried along by
the Government as an incidental to the operation of
the Government-owned synthetic rubber plants. But I
am convinced that when the work is carried on in this
way, with uncertainty as to its continuance, and there-
fore an unusually high personnel turnover, it is not
nearly so effective as if it were part of an over-all co-
ordinated scientific program supported on a more stable
basis.

Another example of an agency of Government which
has recently entered the field of science is the Depart-
ment of State. It has established a science liaison office
and looks fonvard to having scientific attaches serving
in various of our embassies in leading capitals of the
W'orld. I believe that there is an important service to
be rendered in fostering international relations in the
field of science. But I do not believe this can be done
effectively under circumstances where it is just one
minuscule activity under the supervision of men who
are so busy with so many other matters that they are
unable to give it their attention. All such activities of
the United States Government could probably be better
handled by a general science agency, of the kind sug-
gested.

Another recent venture in organization of Govern-
ment science that many feel could be improved is the
Research and Development Board of the Department
of Defense. This was established by one section of the
National Security Act of 1947, the law which estab-

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137

lished a single Department of Defense and was intended
to be the means for bringing about a close coordination
of the scientific research and development work spon-
sored by the Army, the Navy, and the Air Force. Ex-
perience has shown that it has not been a very effective
tool for doing this. I think that this outcome might
have been foreseen from the outset and for the reason
that the Research and Development Board was set up
as a purely advisory body, without operating responsi-
bilities. Operating responsibilities for research continue
to belong to the three services and their individual bu-
reaus. Because the RDB lacks direct responsibility it is
not an attractive place for scientists of real ability to
work, so it has been unable to attract staff of suffi-
cient competence to cope with the very difficult prob-
lems presented by an extremely complicated situation.
I am convinced that the RDB cannot perform a useful
function as long as it functions in a purely advisory
way, and that the situation could be greatly improved
by putting all of the military research laboratories com-
pletely under civilian management of a Department of
Scientific Research or a new Smithsonian Institution.

Next I would like to make a few observations on the
Federal Government as an employer. Uncle Sam is a
reasonably good employer so far as salaries, retirement
plan, vacations, and the like are concerned. But the
salaries paid for positions of major responsibility are
in no way commensurate with the rewards which can
be obtained in private life for similar services. Some
curious inequities develop in this way. The tax position
of many corporations is such that it costs the Govern-
ment more in decreased tax revenues paid by the pri-
vate employers to have a man work in private industry
than the salary which the Government will pay that
man to work full-time for the Government.

The curious thing about the low salary scale which
the Government pays to scientists is that one way and
another the Government is finding it impossible to com-
pete with itself in securing the services of the men it
needs. Many private employers of scientists use them
on Government contract work on a cost-plus basis so
the Government pays the man’s full salary at higher
than Civil Service rates as part of the cost of the con-
tract. This possibility has, in the post-war years, led to
a new development which is having devastating effects
on the ability of Government operated laboratories to
recruit qualified staff. More and more there is a tend-
ency to assign Government research programs to ad hoc
groups organized as private corporations solely for the
purpose of taking a Government contract and even in
some cases for the purpose of staffing and operating a
Government-owned facility. In this way Government
money is used to pay salaries in excess of Civil Service
rates and all manner of operational red-tape is avoided,
but the Government finds itself paying much more for
the same services than it would pay if the work were
done in its own laboratories This is not good for
the morale of loyal Government workers. The proper
remedy would be to improve the rules affecting the
Civil Service instead of inventing ways to evade them.

Aside from questions of salary alone, some members
of Congress so often give expression to attitudes of
contempt and distrust toward the thousands of dedi-
cated, conscientious, and intelligent citizens in the Gov-
ernment service that they have to be quite thick-
skinned indeed not to have their morale in some meas-
ure impaired by such treatment. No private employer
would think of saying the kinds of things about his em-
ployees which are often said about Government em-
ployees and expect to retain any of their loyalty or
devotion. This situation has been greatly aggravated in
recent years by the use of dishonest smear tactics in
Congress giving rise to an artificial hysteria which has
led to widespread injustices toward Government em-
ployees carried out in the name of the Loyalty Pro-
gram. Everyone in Washington knows dozens of stories
of great suffering caused by silly and trivial accusations
in this connection. For example only recently I heard
of a labor relations expert who was employed by our
Government in Japan to work to diminish communist
influence in labor unions there, who was officially com-
mended for his work, and then later had to defend
himself before a loyalty board against the charge “that
when you were in Japan you evinced a great interest
in Communism”. I know of a case of a woman who
was accused of disloyalty on the grounds of sympathetic
association with her own husband. I know of another
who was charged with acquaintance with a scientist
who is in fact the man who is entrusted with a major
role in the hydrogen bomb development.

Not the least of the evils associated with the actual
functioning of the Loyalty Boards is the slowness with
which they operate. Often a person is kept in a state
of nervous suspense for months after a hearing is held
before he gets word of a decision. In general the proc-
esses are carried out in an altogether too formal and
unsympathetic manner. No man can become a psycho-
analyst until he himself has been analyzed. I think the
situation would be improved if no one served on a
Loyalty Board until he had a laboratory course in the
Golden Rule by having himself been given a protracted
experience with a Loyalty Board.

In conclusion let me thank you for your courtesy in
listening to this rather too dogmatically expressed re-
cital of opinions of one who sincerely believes in the
importance of Government service and of science in
the modern world of affairs and who only hopes that
some of these thoughts may make a slight contribution
toward working out some improvements. No one who
has ever been entrusted with major governmental re-
sponsibility can fail to be impressed with the impor-
tance of the American government and of strengthen-
ing the American contribution to the welfare of all the
peoples of the world. I am not an old soldier and I
hope not to fade away. I leave the Government service
happy in the friendships and experience it has given to
me and hoping that I may still in private life be re-
sponsive to the duties of citizenship in this our beloved
America.

138

HISTORY OF PHYSICS

Fifty years of
physics education

PHYSICS TODAY / NOVEMBER 1981 _

A.P. French

A.P. French is a professor of
physics at MIT. He was consult-
ing editor of The American
Journal of Physics from 1973 to
1975 and chairman of The In-
ternational Commission on
Physics Education from 1975 to
1981.

Physics education isn’t what it was
50 years ago. The most obvious
changes have been quantitative:

In 1930 in all of the US about
1000 students received bachelors’
degrees in physics; about 200,
masters’ degrees; and about 100,
PhDs. In 1980 the corresponding
numbers were 4500, 1500 and
1000; and in the peak years
around 1970 the figures were
about 6000, 2500 and 1500 (see
page 52). These large increases,
corresponding to a factor of ten or
more for graduate degrees, also
point to the extent to which physi-
cists have become essential to the
technical development of our soci-
ety and to the increased accep-
tance (at least in principle) of the
idea that every citizen, in today’s
technological society, ought to
have some knowledge of science
in general and of physics in par-
ticular. Few would go so far as to
embrace C.P. Snow’s view that no
person can be considered truly
educated without knowing the sec-

ond law of thermodynamics. (“My
partner doesn’t even know the first
law,” said Michael Flanders, in
mock disgust, in the show “At the
Drop of a Flat.”) But many would
give vigorous assent to what Hen-
ry Perkins1 said in 1969: “As we
are living in a scientific age, phys-
ics is just as much of a cultural
subject as the older humanities.
Not to know something about the
basic principles of mechanics,
electricity and, at least, to have a
smattering of atomic structure
stamps the modern man as only
half-educated, just as ignorance of
Latin and Greek indicated relative
illiteracy to our forefathers.”

The task of the physics teaching
profession is to address both the
professional and the cultural
needs of students; the purpose of
this article is to provide a brief sur-
vey of progress in both areas.

(One place this was done was in
the masterful survey of physics
education in the US as of 1970,
published in 1973 by the National

“P

m

trained, yes, but

not highly trained P

DRAWING BY C. BARSOTTI; © 1980 THE NEW YORKER MAGAZINE. INC.

SOCIAL CONTEXT

139

Academy of Sciences in Physics in
Perspective , Volume 2, Part B.) I
will, however, look only briefly at
graduate physics education. I will
deal mainly with pregraduate
courses in high school and col-
lege. This area, with which I am
most familiar, has changed more
than the relatively stable appren-
ticeship system of graduate train-
ing.

Physics in the
high schools

The most dramatic changes in
physics education in the US during
the past few decades have oc-
curred not in the colleges and uni-
versities but in the high schools,
even though the high schools pre-
sent a numerically far more formi-
dable challenge. During the last
year of secondary school, before
which most US students do not
have access to a physics course,
just over 20%, about 600 000 stu-
dents, take a physics course of
some kind. (My statistics, here
and elsewhere, are based mostly
on data published by the AIP Man-
power Division.) These courses
are taught by about 1 5 000 teach-
ers (of whom, however, it has
been estimated that only about
4000 + 1000 are “adequately
trained for the purpose,” accord-
ing to Clifford Swartz2). Although
these numbers are large, the pos-
sibility of change and reform at
this level is eased by the orga-
nized structure of secondary edu-
cation systems, contrasted with
the near anarchy represented in
2000 independent and largely
autonomous college physics de-
partments.

Two ambitious programs have
transformed the teaching of phys-
ics in high schools; the first was
provided by the Physical Science
Study Committee. Formed in
1956 [before Sputnik I, as its chief
instigator, Jerrold R. Zacharias,
likes to point out), it brought the
methods of big physics research

140

HISTORY OF PHYSICS

The Physics Community — A Retrospective

into the educational domain. Its
goal was to develop a course that
would present physics not as a
catalog of facts and formulas to
be learned, but as an intellectual
adventure concerned with explor-
ing and understanding the real
world. Bringing together several
hundred high-school and college
teachers and millions of dollars
supplied chiefly by the National
Science Foundation, the PSSC
created a completely novel phys-
ics course from scratch, with a full
panoply of teaching aids— text-
books, teachers’ guides, tests, lab-
oratory experiments and appara-
tus, films, and supplementary
monographs. It accomplished
most of the job in about five
years. Nothing like it had ever hit
the educational scene before, but
other sciences were quick to fol-
low this lead.

The PSSC course, the work of
highly respected physicists, of-
fered the US high-school student
(and teacher) a presentation of ba-
sic physics of a sophistication nev-
er before available at that level.
Use of the PSSC course grew rap-
idly at the expense of the old, tra-
ditional courses, until it was being
taken by at least 30% of high-
school physics students.

The PSSC did not, however, re-
alize one of its aims — to increase
the numbers of high-school stu-
dents choosing to take physics at
all. This was admittedly optimis-
tic, since the PSSC course was
acknowledged to be a difficult
one. Could there be another new
course of high scholarly caliber
that would appeal more to the stu-
dent whose interest in physics was
more general? In 1962 Gerald
Holton and his chief collaborators,

F. James Rutherford and Fletcher

G. Watson, at Harvard took up this
challenge. They created Harvard
Project Physics through a major
developmental program very simi-
lar to that used for PSSC. Like
the PSSC, Harvard Project Physics
captured a substantial fraction of
the high-school physics clientele.

In fact, it seems to have come to

be the more popular of the two.
Although it is hard to obtain reli-
able numbers, rough estimates
suggest that these two courses to-
gether reach about 30% of pre-
sent high-school students who
take physics. Their influence,
however, reaches further, for var-
ious features of their approach
have been incorporated in other
widely used high-school textbooks.

Introductory physics at
college and university

According to AIP Manpower Di-
vision statistics, about 350 000 out
of 2 000 000 first-year college stu-
dents take introductory physics in
some form or other. The numbers
may be substantially higher, be-
cause many students take physics
courses in institutions that for var-
ious reasons (lack of a separate
physics department, lack of a
complete bachelor’s degree pro-
gram) are not represented in the
AIP data.

Of the total, something like 5%
take physics courses suited to fu-

ture physicists, chemists and engi-
neers. Another 15% or there-
abouts, including premedical
students and biology majors, enroll
in courses that present physics in
a fairly analytical but mathemat-
ically less demanding way. The
very large remainder — about
80% — engage in a wide variety of
courses that require minimal math-
ematical skills.

With a few exceptions, such as
the Physical Science for Non-
scientists Project, the physics
teaching profession has given or-
ganized attention to curriculum re-
form and innovation more or less
inversely to the size of the various
constituencies identified above.
Admittedly there have been a few
conferences concerned with the
improvement of physical science
courses for liberal arts majors, at
one of which H. R. Crane3 pre-
sented his famous caricature (see
below) of the kind of traditional ap-
proach that repels such students.
Since the early 1 960s, however,
progress has consisted mostly in
the development of a great variety

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field theory at the University of
Rochester.

of new courses by individual in-
structors or departments, here de-
scribed by Arnold A. Strassen-
burg4

“Since 1964 the proliferation of
elementary college physics
courses has been phenomenal.
The need for more diversity to
meet the demands of an in-
creasingly large and varied stu-
dent body was loudly pro-
claimed by several leaders of
the physics education communi-
ty, and these exhortations, with-
out doubt, set the stage for ma-
jor change.

In the late 1960s, however, a
sharp decline in the attractive-
ness of physics as a major pro-
vided a much more powerful
stimulus to seek a new clientele
among students committed to
other disciplines. Offerings
such as “Physics for Poets,”
“The Physics of Music,” and
“The Physics of the Environ-
ment” popped up at virtually ev-
ery college and university in the
US.”

The Commission on College Phys-
ics sponsored conferences and a
summer workshop in 1963 to ad-
dress the needs of the middle
group of students, those going on
to study life sciences. An initial
conference tried to design curricu-
la suited to these students; subse-
quent workshops aimed at produc-
ing materials — monographs,
experiments, computer programs
and films — that could be used in

142

HISTORY OF PHYSICS

these and other curricula. Howev-
er, fifteen years later it is hard to
identify any direct influence of
such efforts on the shape of inter-
mediate-level physics courses.

When it comes to introductory
physics courses for prospective
engineering and, above all, phys-
ics majors, university physics
teachers feel far more confident
about what needs to be done and
are more willing to commit their
time and effort toward the creation
of new courses. There was a
consciousness by the early 1960s
that with the renovation of high-
school physics, led or inspired by
the PSSC program, colleges and
universities needed to upgrade
their offerings. It would have
been irresponsible— and frustrat-
ing to incoming freshmen with im-
proved backgrounds — not to reju-
venate the college curricula. In
fact, some of those who had been
involved in the PSSC— in particu-
lar, Francis L. Friedman, Philip
Morrison and Zacharias— were
among the leaders in pressing for
similar efforts at a higher level.

Among a great wave of curricu-
lum improvement projects during
the 1960s, two projects call for
special mention because of their
sheer size. In 1960, MIT estab-
lished its Science Teaching Center
(later to be called the Education
Research Center) under the direc-
tion of Friedman; less than two
years later, with Charles Kittel as
chairman, the committee formed
that guided the creation of the
Berkeley Physics Course. With
massive backing of the National
Science Foundation, both groups
embarked on large-scale pro-
jects: the Berkeley group, to pro-
duce a set of texts and accompa-
nying laboratory materials; the MIT
group to devise a more diversified
program, which came to include

physics texts as well as films,
demonstrations and student ex-
periments. Notable features of
these projects were an increase in
conceptual and mathematical so-
phistication in the presentation of
physical ideas, an injection of sub-
stantial amounts of “modern phys-
ics” (relativity and quantum ideas)
into the first-year curricula and an
organized use of many different
kinds of learning aids in the pre-
sentation of the subject matter.

In the midst of all these collec-
tive enterprises, a virtuoso perfor-
mance by a single person, Richard
P. Feynman, extended the hori-
zons of every teacher of introduc-
tory physics for prospective ma-
jors. At Caltech from 1961 to
1 963 he gave the lectures that
have become a standard part of
every instructor’s library (see the
photographs on page 54). In his
characteristic fashion, Feynman
thought through everything from
scratch, enriching each topic with
his marvelous insight and original-
ity. The result of Feynman’s ven-
ture was a two-year course cover-
ing all the basic ideas of classical
and modern physics. While it is
too strong meat for all but the very
best students, it provides a pre-
cious resource for teachers of
physics at all levels.

The physics major

The physics major is a multiple
entity. The latest available AIP
statistics show that in 1 978 about
4500 students graduated with
bachelors’ degrees in physics. Of
these, about a third went on to
graduate work in physics, and an-
other quarter into graduate school
in other fields (such as engineer-
ing, mathematics, computer sci-
ence, medicine and law). The re-

mainder, just over 40% of the
graduates, either went directly into
jobs or were planning to do so.

The bulk of these did in fact find
immediate employment; if past ex-
perience is any guide, more than
half made direct use of their phys-
ics training in industry, govern-
ment, teaching, and so on, but a
substantial fraction (perhaps 15%
or more) did not. Therefore, to re-
gard a major in physics as being
primarily a basis for further aca-
demic training in the subject ig-
nores some of the facts.

Recognizing this diversity of in-
terests and career paths on the
part of physics majors, the Com-
mission on College Physics,
founded in 1960 with support by
the NSF (which also funded similar
commissions in other sciences)
helped organize several confer-
ences on undergraduate programs
for physics majors and recom-
mended the creation of two basic
curricula. One curriculum, for stu-
dents going on to graduate study or
work in physics, corresponded clo-
sely to existing programs for physics
majors in most institutions; the other
was for students who would be-
come secondary-school teachers
of physics or would enter other
fields. This latter curriculum would
have been a novel development
had it been completed, but it did not
materialize in any definite or unique
form, although many individual
courses and teaching aids were de-
veloped. With the present decline in
funds for curriculum innovation ac-
tivity in this area has markedly de-
creased.

On top of the retrenchment
forced by shrinkage of resources,
there is a trend to return to older
and more conservative programs.
“Back to Ganot” is a phrase that
has been jocularly applied to this

SOCIAL CONTEXT

143

development, Ganot being the au-
thor of an extraordinarily success-
ful nineteenth-century physics text
that went through many editions in
its original French and then gained
a comparable success in an Eng-
lish translation. Still, one has only
to make a close comparison of
Ganot’s book with a typical text for
physics majors of today to realize
that the growth of sophistication,
the shift from descriptive to analyt-
ical and conceptual, the sheer ele-
vation of levels, has been im-
mense. As Feynman remarked a
number of years ago: “When I
was a student, they didn’t even
have a course in quantum me-
chanics in the graduate school; it
was considered too difficult a sub-
ject. . . . Now we teach it to under-
graduates.”

Tools of the trade

Some of the most notable de-
velopments in physics education
over the past 50 years — and par-
ticularly during the last 25 — have
been in instructional techniques
and aids. I comment on some of
these developments briefly below,
referring especially to the introduc-
tory college level, for which a large
fraction of the innovations have
been designed.

Films. The use of films in phys-
ics instruction has grown tremen-
dously over the last 30 years. The
PSSC gave this trend a great
boost by producing more than 50
films devised and executed under
its control. The films were typical-
ly about 25 minutes in length,
each expounding and demonstrat-
ing a particular topic and designed
to be an integral part of the teach-
ing program.

A number of similar films were

made for use at the college level.
However, because college teach-
ers are in general far less willing
than high-school teachers to sur-
render substantial amounts of
classroom time and their own ini-
tiative as instructors to films of this
type there has been a major shift
to short filmed demonstrations to
be used within the instructor’s own
presentation of a topic. The de-
velopment of 8-mm film-loop pro-
jection has further encouraged the
use of such films, both inside and
outside the classroom, with the re-
sult that there has been a great in-
crease in the variety of physics
demonstrations available to teach-
ers (see figure on page 58).

Some of the obvious advan-
tages of film are its ability to cap-
ture events that occur on too short
or too long a time scale to be
demonstrated directly, are on too
small or too large a scale of size,
or are just too complicated or ex-
pensive to be performed by the
average instructor. Theoretical
problems solved by computer with
a visual display are another ‘natu-
ral’ for presentation on film. The
figures on this page show exam-
ples of filmed demonstrations of
these various kinds.

Television. Although television
is an obvious resource of enor-
mous potential for education, so
far in physics that potential has
gone largely undeveloped. While
this may represent a failure of
imagination on the part of the pro-
fession, there are obstacles to the
effective use of the medium out-
side of such straightforward appli-
cations as the use of closed-circuit
television to feed a lecture to over-
flow audiences or to make visible
a small-scale demonstration.

There are also objections to a
form of instruction that is so frozen

in format and allows for no reac-
tion from the viewer. Perhaps the
biggest obstacle to the expanded
use of television is its sheer cost.

Laboratories. Many years ago
a colleague of mine, at the end of
a freshman lab class that he had
been supervising, remarked to
me: “Well, Ohm’s law has sur-
vived another onslaught!” Such
cynicism about the efficacy of lab-
oratory instruction, at least in intro-
ductory physics courses, is wide-
spread among both teachers and
students. “There is little empirical
evidence,” said Leo Nedelsky at
the beginning of an article about
introductory physics laboratory,5
“that laboratory instruction in ele-
mentary courses contributes sig-
nificantly to the student’s under-
standing of physics. In the
absence of such evidence, phys-
ics teachers argue a priori that
contact with phenomena is a nec-
essary constituent of adequate
training in physics.” Most physics
teachers, probably all, accept that
last proposition; the problem is
how to make the laboratory an in-
structive experience. If this prob-
lem has not been solved, it is not
through lack of effort; more, and
more varied, attention has gone to
laboratory work than to almost any
other component of physics edu-
cation. (See, for example, the re-
port of a 1978 international confer-
ence on the role of the laboratory
in physics education.6)

Technological developments
have certainly brought about dra-
matic refinements in student appa-
ratus. Electronic instrumentation
has improved beyond recognition,
of course. In some cases there
have been reductions in cost. (The
current catalog of one equipment
manufacturer shows two versions
of a free-fall apparatus. One of

144

HISTORY OF PHYSICS

them, a traditional version with a
spark timer and paper tape, costs
well over $1000; a modernized
version with a digital electronic
timer costs less than $200!) The
availability of inexpensive micro-
computer modules has made so-
phisticated instrumentation a pos-
sibility in all kinds of elementary-
laboratory experiments.

For more advanced students,
particularly for physics majors,
there has long been a tradition of
high-quality laboratory work whose
value has been recognized by stu-
dents and teachers alike. For the
most part this has taken the form
of “cookbook” experiments, albeit
of a high order. There has, how-
ever, been a substantial move in
the direction of involving under-
graduates in ongoing research,
which is a healthy antidote to the
abstractness and formality of the
classroom teaching that makes up
the bulk of a student’s training.

Computers. In his AAPT Milli-
kan Award Lecture in 1 978, Alfred
Bork began by saying
“We are at the onset of a major
revolution in education, a revolu-
tion unparalleled since the in-
vention of the printing press.

The computer will be the instru-
ment of this revolution. ... By
the year 2000 the major way of
learning at all levels, and in al-
most all subject areas, will be
through the interactive use of
computers.”

Many physics teachers — includ-
ing some of those for whom the
computer is an essential research
tool— feel almost embarrassed at
the difficulty they have in incorpo-
rating its use into their teaching of
physics. Bork’s belief, implied in
the quotation above, is that the
computer offers an unparalleled
opportunity for students to learn
through interactive dialog. They
can do this at their own paces,
without inhibitions, helped by an

New texts. Above: the PSSC prepared
many films, such as this one showing ripple
tank phenomena (courtesy Kalmia Co.): at
right: the Harvard Protect Physics Course
characteristically used free-hand sketches.

imperturbable instructor of infinite
patience (unless it is programmed
to be otherwise!).

It is Bork’s contention that full
exploitation of the computer as
teacher will serve to humanize,
rather than dehumanize, instruc-
tion by relieving teachers of many
avoidable chores and freeing them
to deal directly with individual stu-
dents. Perhaps this is indeed the
wave of the future, but its accep-
tance in practice will call for a
massive change in the views of
most instructors who, outside cer-
tain centers of enthusiasm, view
the computer’s role much more
conservatively.

One of the most ambitious ef-
forts has been the development of
the plato system at the Universi-
ty of Illinois. Beginning in 1970,
this project has developed instruc-
tional programs for a number of
topics in physics. In addition, it
has provided tutorial materials for
a complete introductory mechan-
ics course, with work by students
at the terminals replacing half of
the lecture time. The system
clearly “works” inasmuch as stu-
dents taking the course in the
plato mode perform at the same
level as those following the con-
ventional route. It does not, how-

ever, seem to demonstrate any
marked superiority.

Some have made optimistic
claims for the use of the computer
in a less dominant role as tutor,
helping students with the solution
of homework problems. For the
present, at least, it seems that this
method, allowing students to de-
termine their pacing, may be the
most effective use of the comput-
er as teacher.

It has been suggested, on the ba-
sis of the time distribution of pub-
lished papers about the use of com-
puters in teaching physics, that
interest in this topic peaked in about
1972 and has since decreased.8
However, this conclusion can be
questioned, even with respect to the
restricted use of the computer as tu-
tor. The more conservative use of
computers for calculations and data
analysis, and as a laboratory instru-
ment, has undoubtedly been grow-
ing steadily.

Keller Plan. In 1968 FredS.
Keller, a professor of psychology,
published a paper with the title
“Goodbye, Teacher ”9 It de-

scribed a scheme by which stu-
dents would proceed at their own
rates through a course, its subject
matter being divided into a number

Stills from films showing
probability distributions for
particle packets on potential
wells. Above: zero surface
thickness: below: surface
thickness of about one-eigth
well width (courtesy Education
Development Center).

-

of separate learning units. In this
scheme, which later acquired the
title PSI (personalized system of
instruction) lectures became sec-
ondary or nonexistent. Students
work from a textbook with guid-
ance from supplementary notes
and tutors and take unit tests
when they feel ready. Testing is
for mastery of the material, and
students do not proceed to a later
unit until they have shown suffi-
cient knowledge of the previous
one. This scheme, enthusiastical-
ly taken up by a number of physics
teachers, has had substantial suc-
cess (as judged by student perfor-
mance) in classes of widely differ-
ent size, all the way from
freshman physics to graduate
courses. It provides the benefits
of immediate feedback (and Skin-
nerian reinforcement) but, as one
of its proponents (Robert G.

Fuller) admits, its influence to date
has been relatively small, perhaps
in part because it involves such a
change of role for the instructor,
who ceases to occupy center
stage, and in part because it may
entail an increased investment of
instructor time to work well. Also,
if a self-paced course in this mode
is competing with other courses
that have strict deadlines and
scheduled examinations, students
are likely to let it slide down their
lists of priorities.

Examinations
and testing

Fragment of a physics oral ex-
amination10 at Oxford University,
about 1890:

Examiner: What is Electricity?

Student: Oh, Sir, I’m sure I
have learnt what it is — I’m
sure I did know — but I’ve for-
gotten.

Examiner: Flow very unfortu-
nate. Only two persons have
ever known what Electricity is,
the Author of Nature and
yourself. Now one of the two
has forgotten.

Devising satisfactory testing and
meaningful evaluation of students
continues to plague physics in-
structors everywhere. It is, how-
ever, a matter that is absolutely
central to the educational pro-
cess. Everyone knows that for
most students the content and
character of examinations come
close to defining their whole atti-
tude to a course. As Eric Rogers
put it in his AAPT Oersted Medal

lecture on examinations in 1969:
“Examinations tell students our
real aims, at least so they be-
lieve. If we stress clear under-
standing and aim at a growing
knowledge of physics, we may
completely sabotage our teach-
ing by a final examination that
asks for numbers to be put in
memorized formulas. Flowever
loud our sermons, however in-
triguing the experiments, stu-
dents will judge by that exam —
and so will next year’s students
who hear about it.”

Students have many pressures on
their time besides the physics
courses we are teaching, and they
know that grades are important in
this harsh world. Few students
(even among those who will be-
come professional physicists) are
so unworldly or so temperamental-
ly secure as to let their interests
wander far afield from what they
can expect to be asked in their ex-
aminations.

Much thought and effort has, of
course, been devoted to these
matters. The PSSC program, for
example, devised a complete set
of tests that emphasized method-
ology of physics and aimed to as-
sess a student’s ability to deal with
novel or unfamiliar situations, to
draw conclusions from given infor-
mation, to make logical predictions
or to suggest new lines of investi-
gation. Another development, the
unit-test system of PSI, uses ex-
aminations as far as possible as
entrance, rather than exit, tests,
such that satisfactory performance
entitles a student to proceed to
the next stage.

The physics teacher

Some essential differences exist
between the advancement of
knowledge in an area of research
and progress in education — in
physics or in any other field. The
basic and obvious point, of course,
is that research is concerned with
the cumulative growth of objective
knowledge, whereas education
means nothing unless it focuses
on the development of the human
individual. As the body of objec-
tive knowledge expands, the prob-
lem of reconciling the needs of the
learner with what is to be learned
becomes ever more acute. Al-
though the nature of the problem
is unchanging, each new genera-
tion has to tackle it afresh. Pro-
gress in education is to be mea-

146

HISTORY OF PHYSICS

sured primarily in terms of the
vigor and imagination with which
this challenge is met. Research
needs to be done on the process
of education itself — a field to
which most physics teachers, at
least at college and university lev-
el, have been far too indifferent.
While physics teachers have their
own subjective impressions of suc-
cessful or unsuccessful teaching
experiences and many institutions
solicit student feedback and evalu-
ation, the matter has received re-
markably little methodical study.
Paul Kirkpatrick, in his AAPT
Oersted Medal lecture in 1959,
commented on this in a provoca-
tive fashion:

“Across the campus from where
you and I work [he was at Stan-
ford] there is a school of educa-
tion, or maybe a department.

We hear that it is there, but we
don’t visit it very often. We are
trying to teach the young and re-
alizing that the job is too hard
for us. Probably there isn't a
teacher here who feels that he
is a complete success. But
while we go on with these feel-
ings of partial success there is
nearby this company of special-
ists in the philosophy and tech-
nique of the teaching process,
and we make no use of them.
When we are stuck on a chem-
istry problem we go to the
chemists; if we get beyond our
depth in mathematics we know
mathematicians who throw us a
rope. ... But when we are won-
dering how to educate we do
not go to the educationists. ... I
cannot dismiss this old boycott,
as some apparently can, by de-
claring that ninety percent of the
educationists are fools led by
the ten percent who are smart
rogues ”

Now don’t imagine that this
pure company is being infiltrated
by a disguised educationist. I
have muddled along for forty
years without the benefit of a
course in education, but I am

not proud of my ignorance as
most science teachers are.
Whether or not the education-
ists know the answers, they deal
with great questions. What is
the real nature of the process of
learning? How can one train
the mind? Can people be
taught to think, and if so how do
you do it? To what teaching
operations are the different
types of students susceptible,
and how are the various types
to be recognized?”

In the past two decades we
have seen physicists, in partner-
ship with educationists and psy-
chologists, beginning to explore
these fundamental questions.
Some are dedicated followers of
Jean Piaget; others, less commit-
ted to particular models of learn-
ing, are simply watching and lis-
tening to what goes on in the
classroom or seeking to under-
stand how students learn by them-
selves through reading, laboratory
experience, and thought.

Experimentation with new teach-
ing strategies has been a promi-
nent feature during the past two
decades. Teachers have been
challenging the complacency of
relying on traditional modes of in-
struction, based primarily on lec-
tures and textbooks. However, in-
novations need to be seen not as
ends in themselves, but as means
to the end of effective teaching
and learning of the subject matter
of physics. John Rigden, editor of
The American Journal of Physics,
commented forcefully on this in a
recent editorial11:

“We [in the AAPT] have allowed
ourselves to become overly en-
amored with one educational
novelty after another. There
was programmed instruction,
the Keller plan, self-paced in-
struction, computer-assisted in-
struction, Piagetian psychology,
and education psychology more
generally. I have been through
them all and in each case the
disciples of the new pedagogical

savior led me up the mountain
to view their promised land — a
promised land that has never
materialized in the form pro-
claimed. Lest I appear curmud-
geonly, I believe all of these
educational strategies have
merit. The good teachers I
have seen use features of all of
them, but they do so without
making a big deal over it. . . . Of
course, a good teacher cares
about students, but that concern
must focus first and foremost on
how the student is responding
to the discipline. A good phys-
ics teacher loves the discipline,
keeps up with the discipline,
knows the discipline, and con-
tributes to the discipline.”
Rigden’s remarks concern phys-
ics teaching and teachers in col-
leges and universities, where im-
provement is needed but calam-
ities aren’t widespread. At the
high schools, however, there are
causes for major concern. I cited
earlier the estimate that only about
a quarter of the approximately
15 000 teachers who teach phys-
ics in high school are “adequate-
ly” trained for the job. Far too of-
ten the teaching of physics is a
minor assignment for a teacher
whose main responsibilities and
whose own training are in a differ-
ent field. Furthermore, the great-
er material rewards of industry are
drawing away many of the most
able teachers: Only about 5% of
new recipients of masters’ de-
grees in physics now go into high-
school teaching, compared with
about 20% a decade ago. While
it always has been a rarity for a
person with a good degree in
physics to go into teaching at the
precollege level, the recent trend
is alarming.

The role of the NSF

No account of progress in phys-
ics education in the US would be
complete without reference to the

* i Lay

a 'v

1 >

Physics labs of the

past at Brown (far left)
and at Wellesley (near
left) and of the present
at Carleton courtesy
the AIP Niels Bohr
Library.

role played by the National Sci-
ence Foundation.

Almost immediately after its cre-
ation in 1950, the NSF launched
its graduate fellowship program, its
first major contribution to science
education. In the first full year of
operation (FY 1952) this program
accounted for $1.5 million out of a
total appropriation of $3.5 million
for the Foundation’s work; the
Foundation funded over 500 pre-
doctoral fellowships (in all
branches of science). The pro-
gram grew rapidly, until by the
mid-1960s it was supporting well
over 3000 predoctoral students
through fellowships or trainee-
ships; about a third of them at this
point were in the physical sciences
(about 10% in physics in particu-
lar). From 1967, when a maxi-
mum of $45 million per year was
reached, student support declined
rapidly. By 1 975 the allotment of
funds was down to about $13 mil-
lion (equivalent to only about $8
million in 1967 dollars). The de-
cline for physics was even more
rapid, since the fraction of the fel-
lowships awarded in the physical
sciences was also sharply re-
duced. The total demise of such
support is now imminent. The
impetus the NSF gave to graduate
education through its graduate fel-
lowship programs has certainly
been of enormous value; its elimi-
nation is to be deplored.

A similar story describes the
NSF’s support of other aspects of
science education, which began in
a major way in 1956-57, with the
PSSC program and the summer
institutes for science teachers.

The latter, supplemented by aca-
demic-year institutes, fellowships
for science teachers, and so on,
rapidly became a major compo-
nent of NSF’s science education
budget; by the early 1960s the
NSF was supporting the institute
programs at a level of over $40
million per year, that is, about two-
thirds of the total funds then being
allocated to science education
(excluding the graduate fellowship
programs). These institutes and
various related programs brought
large numbers of secondary-
school teachers into contact with
teachers from colleges and univer-
sities, which was very beneficial to
both groups and to the health of
science education generally.

As time went on, the Foundation
expanded and diversified its pro-
grams of aid to science educa-
tion. In 1965, the total support for
such programs had risen to about
$80 million per year; of this, nearly

NSF Support of science
education programs

1967 constant dollars

NSF funding for (top)
predoctoral fellowships and
traineeships in which the dotted
line indicates figures in 1967
dollars; (middle) science
education programs; (bottom)
science education as a
percentage of total NSF
budget. Data from NSF annual
reports.

-

a NSF Support of science education
/\ as percentage of total NSF budget

I \ (Predoctoral fellowships & traineeships excluded)

-

J

1 1

1

60% went into institutes and other
teacher-improvement programs,
about 20% into course content
and curriculum development, and
about 20% into direct aid to col-
leges and schools (in a ratio of
roughly 4:1) for scientific equip-
ment.

The middle graph on page 61
shows the total of NSF support for

science education (excluding pre-
doctoral fellowships and trainee-
ships) as a function of time. It
may be seen that, corrected for in-
flation, the NSF did not maintain
support at the level of the early
1 960s. By 1 980 support was
down to about one-third of that
peak. Even more striking is the
bottom graph on page 61 , which

shows NSF support of science
education expressed as a percent-
age of the total NSF budget; clear-
ly the support of education has
lost a great deal of ground relative
to research.

It is true, of course, that even
after the cutbacks, the level of
NSF support for science education
in FY 1980, at about $60 million
per year, was by no means negligi-
ble. There were summer courses
and academic-year workshops
reaching over 1 5 000 teachers for
grades 5-12 and short courses for
3000 faculty members at two-year
and four-year colleges. About
18% of the total program funds
went to direct support of minor-
ities. “Science and society” pro-
grams received $7.3 million (more
than 10% of the total), and nearly
$14 million went into science edu-
cation and research, much of it for
the development of instructional
techniques and materials and for
research into the learning pro-
cess. The emphasis has thus
shifted markedly from the earlier
days, when scientific subject mat-
ter and curriculum development
loomed large and broader social
concerns were hardly considered.
These statistics for NSF support of
science education in general apply
with an appropriate scaling factor
to physics in particular.

The importance of NSF contri-
butions cannot be overestimated;
they have been used, as we have
seen, for major curriculum im-
provement projects, for upgrading
of physics facilities at the secon-
dary and college levels, for the ac-
tivities of the Commission on Col-
lege Physics, for extensive teacher
training and for many other
things. As with the graduate fel-
lowships, the erosion of this sup-
port must be regarded as a seri-
ous blow to the state of physics
education in the US. The pros-
pect that the present Administra-
tion might phase out all the funds
for such activities is grim indeed

and suggests a strange view of
priorities in a society whose health
is so directly based on scientific
achievement.

Problems and prospects

This article will, I hope, have jus-
tified the belief that there is indeed
progress in physics education—
and, more, that it is at present a
field of great activity and perhaps
of more diversity than ever be-
fore. If the problems confronting
us seem much the same as those
of 50 years ago, that is no cause
for despair — it is in the nature of
the subject. Flowever, it would be
wrong to pretend that all is rosy;
among the areas in special difficul-
ty are these:

► The health of the teaching pro-
fession itself. Except for the col-
lege and university level, the edu-
cational system is not producing
an adequate supply of new, com-
petent teachers; in the past year
alone, the membership of the As-
sociation of High School Science
Teachers decreased by 10%.
There is also a serious lack of
contact between teachers at dif-
ferent levels, in particular between
teachers at secondary schools
and universities. The wave of ac-
tivity in this direction during the
1960s, sponsored mainly by the
National Science Foundation, has
subsided with the fading of that
support.

► The lack of success teachers
have had in communicating know-
ledge or appreciation of physics to
students who are not going to be-
come professional scientists. This
difficulty has its origins at the earli-
est levels of education, well before
students have the chance to elect
(or, more often, reject) physics as
a subject of study toward the end
of high school. Physicists (and
other scientists) are not succeed-
ing in spreading scientific literacy;
they are best at producing their

Students at Garden City High
School recording observations
in a physics lab (courtesy AIP
Niels Bohr Library).

own successors.This must be
seen as a most urgent problem in
our society because, until it is
solved, there will be a continuing
gulf preventing understanding be-
tween scientists and the public, in
which latter category are many in
positions of power and responsibil-
ity.

* * *

I wish to thank Susanne D. Ellis for sending
me a quantity of statistical data from pre-
vious and current AIP Manpower Surveys
and E. L. Jossem for communicating a
number of materials and suggestions per-
taining to this article.

[Note added, February 1 985:

Since this article was written, one
major development has been the re-
establishment (in October, 1983) of
the Science and Engineering Edu-
cation Directorate within the NSF,
with particular concern for pre-col-
lege programs, in response to wide
recognition of a crisis in science and
mathematics education in the U.S.
(In this connection, see the special
issue of Physics Today, September,
1983.)

At the graduate level, the feared
elimination of NSF fellowships did
not in fact take place, and this pro-
gram has been maintained since
1981 at a fairly constant level.]

References

1. Henry A. Perkins, Am. J. Phys. 17, 376
(1949).

2. Clifford Swartz, The Physics Teacher
17, 422 (1979).

3. H. R. Crane, Commission on College
Physics, Newsletter No. 7, April 1965.

4. Arnold A. Strassenburg, Change 10, (D
50 (1978).

5. Leo Nedelsky, Am. J. Phys. 26, 51
(1958).

6. The Role of the Laboratory in Physics
Education. J. G. Jones, J. L. Lewis,
eds., Association for Science Educa-
tion, Hatfield, UK, 1980.

7. S. G. Smith and B. H. Sherwood, Sci-
ence 192, 344 (1976).

8. A. Douglas Davis, Am. J. Phys. 49, 391
(1981).

9. Fred S. Keller, J. Appl. Behavior Anal.

1, 79 (1968).

10. Falconer Madan, Oxford Outside the
Guide-Books, in Jan Morris, ed., Ox-
ford Book of Oxford, Oxford U. P.,
1978.

11. John Rigden, Am. J. Phys. 49, 809

(1981). □

SOCIAL CONTEXT

149

Women in physics:
unnecessary, injurious and
out of place?

Despite eight years of affirmative action
more changes are necessary to create an atmosphere where
women are equally accepted in the field of physics.

Vera Kistiakowsky physics today / February i98o

The subtitle for this article is taken from
a Strindberg essay written at the end of
the 19th century opposing the appoint-
ment of the mathematician, Sonia Kova-
levsky, to a professorship at the Univer-
sity of Stockholm, in which he attempts
to prove “as decidedly as that two and two
make four, what a monstrosity is a woman
who is a professor of mathematics, and
how unnecessary, injurious and out of
place she is”.1 It is certainly a much more
extreme statement than anything likely
to be voiced publicly today but it does
vividly and tersely encapsulate many of
the opinions that have been expressed to
me in much more veiled and discursive
form over the last ten years. Largely
because of these continuing though muted
attitudes I have accepted an invitation to
write this article for PHYSICS TODAY. I
will very briefly sketch the history of
women’s participation in physics as a
background to the current situation and
then discuss some statistical information
about women physicists in the recent past
and present in the United States. It will
come as no surprise that the percentage of
physicists who are women is small and
that their employment patterns are dif-
ferent from those of men. I will discuss
the possible reasons for this situation.
Finally, I will comment briefly on recent
changes and what expectations one may
have for the future.

History from Arate to Whiting

Since physics as we know it today only
emerged at the beginning of the seven-
teenth century, I should perhaps start my
mention of women’s participation with
this period. However, having grown up

Vera Kistiakowski is a professor of physics at
MIT and does research in experimental high-
energy particle physics.

with a pre-history of science, that of the
Greek natural philosophers, in which
women were conspicuous by their ab-
sence, I can not resist remarking that
there is evidence that women natural
philosophers did exist. Arate of Cyrene
was supposedly a contemporary of So-
crates (5th century BC) who taught and
wrote on natural philosophy in Attica.1
She was, however, not the first; women
were equal members of the Pythagorean
school in the 6th century BC2 and Thea-
no, the wife of Pythagoras, assumed the
leadership of the school after his death.3
Moving forward a millennium we find
Hypatia, a neo-Platonic philosopher and
mathematician who spent the last part of
her brief life teaching at the university in
Alexandria at the beginning of the 5th
century AD.3 In the middle ages the
physical sciences languished; and, al-
though the convents produced a numbei
of notable women scholars, their writings
were mainly in the areas of the biological
sciences and medicine. However, one of
these women, St Hildegard, the Ben-
edictine Abbess of Bingen-on-the-Rhine
in the 12th century AD, wrote on a helio-
centric universe in which “the sun attracts
the heavenly bodies as the earth attracts
its inhabitants,” an early intimation of
gravitation.1

Unfortunately, the beginning of the
scientific age coincided with a wave of
opposition to the education of women in
Europe and Great Britain. The few
women who contributed to physics were
either of high enough social status that
they could follow their inclinations de-
spite the general prejudices of the times,
like Emilie de Breteuil, Marquise du
Chatelet and Laura Bassi, of the early
18th century1'3, or like Mary Somerville
(early 19th century), who was known
principally as a mathematical astronomer,

self-educated over the opposition of their
families. This situation remained about
the same until the end of the 19th cen-
tury.

In the US the situation of women im-
proved somewhat more rapidly than it did
elsewhere. The Boston public schools
were started in 1642, and although they
did not admit girls until 1789, this oc-
curred considerably earlier than was the
case in Europe and Great Britain. Many
secondary schools in the US were opened
to women at the beginning of the 19th
century, apparently because more school
teachers were needed. Finally, in 1837,
two hundred and one years after the
founding of Harvard College, Oberlin
College admitted the first three women to
the bachelor’s degree program.5 Due to
both the economic and feminist pressures
for women’s education, a few more male
institutions became coeducational, and
several women’s colleges were established.
However, the number of these institutions
remained small until after the Civil War,
and many of the women’s colleges were of
inferior quality. The lack of greater
change in opportunities for women could
be considered part of a general pattern
where educational reforms which in-
cluded the establishment of scientific,
technical and graduate education re-
mained blocked until after the war ended
in 1865. Then both academic science and
women’s education blossomed and the
numbers of women scientists increased.
We know of no woman recognized as a
physicist prior to this period; the earliest
woman scientists in the US of whom there
is a record were a botanist, Jane Colden
(1724-66), and an astronomer, Maria
Mitchell (1818-89). Two of the first
women to achieve recognition as physi-
cists were Margaret E. Maltby (1845-
1926) and Sarah F. Whiting (1847-1927),

150

HISTORY OF PHYSICS

“/ ivant you to know, gentlemen, that at this moment I feel

1 have realized my full potential as a woman."

Drawing by Franscmo, © 1973 The New Yorker Magazine, mo

who taught at Barnard and Wellesley
College respectively.4

Women physicists in the USA

Margaret Rossiter6 has given us a very
detailed picture of the situation of women
scientists in the US at the beginning of the
20th century using the information given
for individual men and women in the
1906, 1910 and 1921 editions of “Ameri-
can Men of Science.” Among the physi-
cists included in her sample are 23
women, a number that corresponds to
2.6% of the total number of physicists
listed. It is not surprising that 1 1 of these
women received their undergraduate ed-
ucation at women’s colleges and that 21 of
them were employed at women’s colleges
at some point in their career. These col-
leges were both an important source and
the employer of a majority of academic
women at the beginning of the century.
Three of the women also spent extended
periods of time as secondary school
teachers, whereas this was true of none of
the men, another difference common in
fields other than physics. None of the
women physicists had married. It was
generally accepted before 1920 that the
pursuit of a scientific career required a
single-minded determination, which was
incompatible with marriage for a woman.
A wife was expected to be totally dedi-
cated to that role and to subordinate her
interests and activities to the aspirations
of her husband.

By the end of the 19th century the PhD
had become the scientific union card, and
one may begin to trace the participation
of women in physics through the per-
centage of doctorates awarded to women.
In Rossiter’s sample, 65% of the women
and 71% of the men physicists had PhD’s.
The percentage of physics doctorates
awarded to women increased until 1920,

a year in which four women received
physics PhD’s, 19% of a total of 21. 7 The
figure on page 34 gives the number and
percentage of physics doctorates awarded
to women from 1920 to 1978. The corre-
sponding numbers and percentages for
astronomy doctorates are also shown be-
cause some of the statistical information
I will discuss later in this paper is avail-
able only for physicists and astronomers
lumped together. It can be seen in the
figure that the percentage dropped
steadily to a low of 1.8% in the 1950’s.
The numbers of women physicsts in-
creased in this period, but less rapidly
than was the case for men. The reasons
for this pattern, which is also seen in most
other fields, include the subsiding of the
first wave of feminism, which exhausted
itself on the achievement of suffrage and
universal education in the early 1920’s.
The improvement of women’s role in
marriage, which also occurred, was not
far-reaching enough to make marriage
and career generally compatible. The
depression that followed was a further
deterrent to the aspirations of women; any
money available in a family was usually
dedicated to the education of the men,
who were still considered the primary
breadwinners. And in World War II, al-
though women went to work by the mil-
lions, graduate study did not seem an
appropriately patriotic endeavor. After
the war the massive return-to-the-home
propaganda campaign presented the
women of my generation with a clear and
explicit message — husband and family
came first and this should be the exclusive
concern of women. The decline contin-
ued, reaching a low point in the 1950’s. In
the 1960’s, when physics was mushroom-
ing in post-Sputnik euphoria, the per-
centage of doctorates awarded to women
began to increase, probably due to the

many changes of that decade which af-
fected social attitudes, and marital and
economic patterns. These include the
resurgence of the feminist movement
which became increasingly vigorous in the
later 1960’s, leading to further changes
reflected in the continuing increased
percentages for women in the 1970’s.

The 1973 New Yorker cartoon in the
figure on this page very accurately por-
trays this change. The phraseology of its
caption is that used to describe the wo-
manly woman who was the paragon in the
previous three decades, which sounds
wildly inappropriate when applied to
success in a mostly masculine field.

This renaissance of feminism was felt
by professional women and led, among
other things, to studies of the situation of
women in the various professional so-
cieties in the early 1970’s. In The
American Physical Society, Brian
Schwartz started the ball rolling.
Through the Forum on Physics and So-
ciety, he organized a session on Women in
Physics, chaired by Fay Ajzenberg-Selove,
at the 1971 Annual Meeting of the APS.
This was a most thought -provoking oc-
casion, not only because of the presenta-
tions by the speakers but also because of
the less than informed comments from
some members of the audience. The
most memorable was the statement, “If I
had been married to Pierre Curie, I would
have been Madame Curie,” by a well-
known male physicist. This session in-
spired a letter cosigned by 20 women
physicists requesting that the APS
Council establish a committee on women
in physics to study their situation and
make recommendations for appropriate
actions by the Society. At the 1971
spring meeting in Washington the Council
did establish such a committee and with
the help of Jerome B. Wiesner, president

SOCIAL CONTEXT

151

of Massachusetts Institute of Technology,
it obtained the Sloan Foundation grant
that made the study possible. A report
and a roster containing the names of
women physicists were prepared and
submitted to the APS Council at the 1972
annual meeting.7 Seven years of affir-
mative action later we are all, perhaps,
accustomed to the statistics, but at the
time it was novel information. For ex-
ample, an eminent physicist whom 1 en-
countered at an information-gathering
session of the Committee on the Future of
the APS asked me why the Committee on
Women in Physics was wasting its time on
a study when there were only two women
physicists in the United States and both
of them were happy. Obviously, he was
aware that there were more than two.

However, most physicists would have
numbered their women colleagues in the
tens and not in the hundreds, which was
the outcome of the study. He was also
misinformed on the question of happi-
ness. One of the women he had in mind
was a member of the Committee, the
other was actively supporting it, and
neither was happy with the status quo.
Only two of the 451 doctoral women
physicists who responded to the survey
indicated any lack of enthusiasm for the
work of the Committee, and a majority of
the respondents were strongly supportive.
This interest of many women physicists
in the issues raised has continued to be
active and the Committee has therefore
continued with a changing membership
carrying out a variety of projects.

Let me briefly summarize the findings
of the 1971 study. It described a situation
that was little changed from that de-
scribed by Rossiter for the period before
1920. Women physicists in both studies
were employed mainly in academia, were
found more frequently in the lower fac-
ulty ranks and non-faculty positions, and
worked at the less prestigious institutions.
In both studies a larger percentage of
women than of men were found to suffer
from involuntary unemployment and
under-employment, and the average sal-
aries of employed women were lower. An
interesting difference between the situa-
tion in 1971 and that before 1920 is that
60% of women physicists in 1971 were
married, compared with none in 1920.
The APS study drew the conclusion that
overt discrimination, prevalent societal
attitudes and the practical problems of
combining career and marriage had
played important roles in causing the
differences observed between the women
and men who had chosen physics as a ca-
reer.

The situation in the 1970’s

Let us look briefly at the statistics for
the participation of women in physics
during the last eight years. The figure on
page 34 shows that the number and per-
centage of doctorates awarded to women
have continued to increase since 1971 but
the percentage increase is much more
dramatic. This has been partly due to the
continuing increases in the number of
bachelor’s degrees in physics awarded to
women (see the figure on page 36) and
also because the fraction of women stu-
dents leaving graduate study with only a
master’s degree has decreased. Thirty-
three percent of the women receiving
physics baccalaureates in the 1950’s went
on to a master’s degree within an average
period of two years and 37% did so in the
1960’s. The ratio of the percentages is
1.12, indicating only a small (12%) in-
crease. However, the comparable figures
for those completing a doctorate an av-
erage of seven years later were 10% for
those receiving baccalaureates in the
1950’s and 17% for the 1960’s, a 70% in-
crease.

The percentage of the doctorates
awarded to women in the various sub-
fields of physics in the periods 1960-69
and 1970-76 were not significantly dif-
ferent from those for all subfields com-
bined in those periods, respectively 1.9%
and 3.5%. This percentage includes as-
trophysics in the later period (4.9 ± 1.0%).
The percentage of the doctorates in as-
tronomy awarded to women in 1970-76
was significantly higher (8.4 ± 1.4%), as
was the percentage of doctorates in as-
tronomy and astrophysics combined in
1960-69 (6.4 ± 1.2%). However, since the
astronomy doctorates were only about 5%
of the number awarded in astronomy and
physics combined in both periods the
statistical information for these combined

1920 1930 1940 1950 1960 1970 1974 1978

YEAR

Doctoral degrees awarded to women. From 1920 to 1970 the numbers are averaged over and
the percentages are calculated for each decade. From 1970 to 1978 the physics numbers are
averaged over and the percentages are calculated for each two year period. The astronomy number
is averaged over and the percent is calculated for the eight year period. These data are taken from
“Doctorates Awarded from 1920 to 1971 by Subfield of Doctorate, Sex and Decade," National
Research Council (1973) and "Summary Report (Year). Doctorate Recipients from United States
Universities," National Academy of Sciences, for the Years 1972 through 1977.

152

HISTORY OF PHYSICS

fields will not be significantly different
from that for physics alone.

Some further comments are possible
concerning the physics and astronomy
doctorates of recent years. For example,
63.3% of the women and 63.5% of the men
receiving doctorates in 1974 through 1977
were married, reflecting the very major
change in attitudes toward the possibility
of combining careers and marriage since
the beginning of this century.8 In the
years 1973 through 1975 11% of the black
and American Indian doctoral recipients
were women, a percentage which is based
on very small numbers and is, therefore,
not significantly different from the cor-
responding percentage for whites, of
whom 3.4% were women. However, the
percentage of foreign citizens awarded
doctorates in the years 1974 through 1977
who were women is 7.7%, which is signif-
icantly higher than 4.2%, the corre-
sponding percentage for US citizens.8 In
this period both the median age when
receiving the doctorate and the median
length of time between baccalaureate and
doctorate were the same for men and
women.8

The percentage of doctorates in the
physics/astronomy labor force (those
employed or seeking employment) who
were women rose from 2.0% in 19717 to
2.5% in 1975.® The percentage of women
who were foreign-born US citizens or
foreign citizens in the labor force in 1975
was 21.8%, which is not different within
the uncertainties from the percentage,
20.6%, for men.® The table at the top of
this page indicates that the percentage of
women employed part time or full time
was 89% in 1973, whereas the similar
percentage for men was 97%. The per-
centage of those unemployed and seeking
employment was about four times greater
for women than for men. Approximately
eight times more women worked part
time, but in 1973 about half of them were
seeking full-time employment. In 1977
the percentage of women doctorates in
physics and astronomy in the labor force
who were seeking employment was 5.7%,
still much higher than that for men.10
However, between 1973 and 1975 the
percentage of women doctorates in
physics and astronomy who were working
part time and seeking full-time employ-
ment dropped from 8.4% to 2.7%, al-
though it was still more than three times
greater than the corresponding percent-
age for men.11

The table at the bottom of this page
gives the distribution of men and women
physicists and astronomers with respect
to type of employer. The percentage of
women in educational institutions in 1973
was greater than that for men, but de-
creased from its 1971 value of 77%, with
corresponding increases in the percent-
ages in government and nonprofit em-
ployment.7 The percentage of men in
industry decreased from 26% in 1971,
whereas that of women increased very

slightly.7 It should be noted that the
percentages of doctoral women who
taught in junior colleges and secondary
schools in 1973 are larger than those for
men. However, a study of women high-
school physics teachers showed that these
women are a small minority and, in fact,
most women high-school physics teachers
do not have any physics degree.12

The median salaries for men and
women for the various types of employers
were consistently lower for women by 5 to
20% in 1971, 1973 and 1977 T10 In any
number of studies it has been found that
further subdivisions of the sample does
not remove the differences. For example,
in 1977 the median salaries for all age
groups of women doctorates including the
youngest were significantly less than
those for men.10

Because the major employer of physi-
cists is the educational institution, it is
interesting to examine the situation there
more closely. The table on page 37 pre-
sents the number and percentage of
women in various types of physics de-
partments in 1971—72 and in 1978-79. It
is seen that the percentages for the total
of all types of departments have de-
creased except for assistant professors
and “other.” In the PhD-granting de-
partments the changes are not significant
except for assistant professors. The in-
creases in the percentages in the “Top
Ten” physics departments are particu-
larly striking but should be interpreted
with caution since seven of the eleven
women are at MIT. Similarly, although
7.3% (ten women) of all the assistant
professors appointed between 1972 and
1979 in these ten departments were
women, the figure drops to 4.4% (five
women) for the nine departments ex-
cluding MIT. It should be noted that
except for the “Top Ten” category, the
institutions in the various categories are
not exactly the same in the two years
studied, and thus the changes in per-
centage and number are a composite of
changes in degree-granting type and
changes in the employment of women.
Eight years of affirmative action can
hardly be said to have caused major
changes in the presence of women on
physics-department faculties. None-
theless, there has indisputably been an
improvement for women at the assis-
tant-professor appointment level.

In summary, the predominant im-
pression gained from looking at the sta-
tistics is that there has not been very
much change since the beginning of the
century or since the 1971 APS study.
The exceptions are the continuing in-
crease in the percentage of PhD’s awarded
to women and presence of a few more
women on the faculties of departments in
research universities.

Reasons and remedies

If one wishes to speculate on the future
it is important to consider the reasons for

Employment status of Men and
Women PhD

Physicists and Astronomers in 1973

Employment Status

Men

Women

Full-time

94%

66%

Part-time

1.7%

16%

Part-time seeking full-

0.8%

7%

time

Unemployed seeking

1.7%

7%

employment

Unemployed not

3.0%

11%

seeking, retired, other

Total number in sample

17 481

471

Data from 1973 Survey of Doctoral Scientists and Engineers,
National Research Council.

the low participation of women in physics
and for the differences between the ca-
reers of men and women. I will discuss
various reasons that have been suggested,
grouping them into five categories: in-
nate ability, environment, discrimination,
career conflicts, and the Matthew effect.
I will also comment on remedies.

The question of an insurmountable
difference in innate ability between the
sexes has become somewhat of an un-
mentionable topic these days, thanks to
the raised level of public sensitivity.
There are few Lionel Tigers who will
argue in the public press that since males
dominate the baboon society, females
must be subordinate in human society.13
However, there are many studies inves-
tigating sex differences in various attrib-
utes, and it is necessary to deal with this
topic by taking a close look at the situa-
tion concerning innate and unalterable
sex differences. It has been difficult for
a non-specialist to get a clear picture of
the cumulative outcome of such studies
due to the prolixity of the experimental
situation, but there is now an encyclo-
pedic compilation and discussion of this
research by Eleanor Maccoby and Carol
Jacklin.14 Although there is not universal
agreement with all of the conclusions
drawn by the authors, their overall picture
is generally accepted and disagreement is
focused on interpretation of experiments
in certain areas. The tabular arrays of
experimental results presented in Mac-

Employers of Men and Women PhD
Physicists and Astronomers in 1973

Employer

Men

Women

Educational Institution

56%

67%

PhD Granting

41%

44%

MA Granting

5%

4%

BA Granting

9%

15%

Jr College

1%

3%

Secondary School

0.3%

1%

Government

15%

16%

Industry

21%

10%

Nonprofit

5%

4%

Other

3%

3%

Total Number

16 689

387

Data from 1973 Survey of Doctoral Scientists and Engineers,
National Research Council.

SOCIAL CONTEXT

153

coby and Jacklin’s book clearly make the
point that the result of a single experi-
ment, or those of a small group of experi-
ments, are never adequate to yield a de-
finitive answer to any general question in
this field. The sample choice, the ex-
perimental technique and the interpre-
tation of what is measured permit con-
tradictory results for any attribute stud-
ied. However, certain patterns do emerge

and they are relevant to aptitude for sci-
entific work. First of all, there are eight
attributes for which sex differences are
commonly believed to exist but for which
the evidence is conclusive that this is not
the case. These include rote-learning
ability, higher-level cognitive processing,
analytic ability and achievement moti-
vation. For all of these no sex differences
of any origin have been found. For seven

other attributes, including competitive-
ness, dominance and compliance, Mac-
coby and Jacklin conclude that there is
not sufficient evidence to decide the
question. They also conclude that there
are four areas where sex differences are
well established. F or two of these, verbal
ability and mathematical ability, available
evidence does not indicate a sex-linked
genetic component, and the sex differ-
ences can be attributed completely to
environmental effects. The magnitude
of the sex differences in mathematical
ability varies widely, depending on the age
group studied, from none for young chil-
dren to significant differences for adults.
The differences between medians of the
relevant test scores for men and women
are at most 0.4 of the standard deviations,
and the test score distributions extend
over the whole range of values for both
sexes.

Finally, there are two attributes for
which Maccoby and Jacklin believe evi-
dence exists for a sex-linked genetic
component. The first is aggression,
which is probably not positively corre-
lated with scientific competence since, as
it is defined, it does not include achieve-
ment motivation, competitiveness or
dominance. Furthermore, since the
learned component of this attribute is
important and aggression is negatively
correlated with intellectual ability in boys,
the greater male biological priming for
learning aggressive behavior appears to be
a negative indicator for a male scientific
career. It is interesting to note that the
correlation is positive in girls and that
aggressiveness could be a positive indi-
cator in their case.

The second attribute for which the
authors believe there is evidence for a
sex- linked genetic difference is one type
of visual-spatial ability. There is some
disagreement with this assessment, but,
even if it is correct, it only means that one
of a number of genes contributing to high
spatial ability is sex-linked. Further-
more, there is also an equally important
learned component to the exercise of
these abilities. The differences observed
between the medians of relevant test
scores for males and females vary widely
between various cultures and are at most
1.4 of the standard deviations. Since
there is no information concerning the
correlation of spatial ability with scientific
achievement it is hard to assess the effect
of this attribute. However, it is clear that
the one sex-linked genetic component is
not a major factor and that the differences
could be substantially reduced by an ed-
ucational process which stresses devel-
opment of visual-spatial abilities equally
for both boys and girls.

Thus, it is extremely unlikely that
sex-linked genetic differences are an im-
portant factor in the observed differences
in scientific participation. There remain,
however, the differences that are envi-
ronmental in origin, and their importance

Bachelor's and master's degrees awarded to women. The numbers were averaged over and
the percentages calculated for the periods 1948 to 1960 and 1960 to 1970. Annual numbers and
percentages are given for the period 1970 to 1976. These data are taken from Table PS-P-2,
“Professional Women and Minorities,” B. M. Vetter, E. L. Babco and J. E. Mclntire, Scientific
Manpower Commission, Washington, D.C. (1978).

154

HISTORY OF PHYSICS

is evident. It is impossible to establish
cause and effect, but I would suggest that
the same environmental pressures that
have led to the differences on mathe-
matical ability test scores are also re-
sponsible for the sharp decrease in the
participation of girls in mathematics and
physical-science courses in secondary
school with the level of the course, rather
than mathematical ability itself. The
difference in participation is much too
great to be plausibly accounted for by the
small differences in the medians of the
test score distribution. What are these
pressures? They start in early childhood
when girls are rewarded for “feminine
behavior” and given “girl’s” toys. They
escalate in adolescence when conformity
to a particular feminine role is considered
necessary to attract boys. To be good at
science and math has been considered to
be inappropriate for a girl, a threat to her
popularity and unnecessary for her future
role in society. Alison Kelly has pointed
out in a paper describing the substantial
differences in participation in secondary
school physics in Great Britain, that girls’
schools have a significantly better record
than coeducatipnal schools, presumably
because in that environment there is more
faculty encouragement and peer support
for achievement in physics.15

These effects are also felt at the un-
dergraduate college level, where women’s
participation in physics continues to be
low in spite of the academic selection that
has taken place. In general, a lower per-
centage of women than men prepare
themselves for graduate school in any
discipline. The seven women’s colleges
that are linked with the Ivy League men’s
colleges (The Seven Sisters: Barnard,
Bryn Mawr, Mount Holyoke, Radcliffe,
Smith, Vassar and Wellesley) have a
uniquely excellent record for both the
number and percentage of their graduates
who have continued to a doctorate and to
professional recognition.16 This record
includes the fields of mathematics and the
physical sciences, and one can again
speculate that a supportive environment
is a cause.

That self-selection also plays a role is
evident from the excellent record of a few
coeducational colleges (Oberlin, Reed and
Swarthmore) and from the fact that a
greater percentage of women with bac-
calaureate degrees from MIT later re-
ceived a doctorate degree than was the
case for any other academic institution
with a significant number of women (11%
versus 9.7% for the next highest).17 This
could hardly be attributed to a reputation
for a supportive environment, since, al-
though MIT granted its first degree to a
woman in 1867, it was not until nearly one
hundred years later that women were
recognized as an important part of the
undergraduate community. However,
my own experience and that of many
other women has been that the supportive
environment of a woman’s college made

it much easier to study mathematics and
science with the expectation of pursuing
careers in these diciplines.

The question of math and science
avoidance has been discussed by many
authors, notably Shiela Tobias,18 and a
number of programs to counteract this
situation have been established. One of
these is an informal network of women
scientists and mathematicians working in
San Francisco area schools and colleges to
encourage girls to take science and math
courses and to tell them about career op-
tions in the various fields. The program,
originated primarily by Lenore Blum and
Nancy Kreinberg, presently involves more
than 400 women scientists and mathe-
maticians.19

Societal views of appropriate roles for
women are changing. Admittedly, the
progress is uneven, but I do not think that
there can be a pre-teenage girl whose
family owns a television set who views
marriage and motherhood as the only
option for a woman, even though this may
be the only option of interest to her. She

knows that there are women in many
“men’s” fields, including the physical
sciences, and gradually this should result
in increases in the numbers of girls who
take physical sciences and advanced math
in high school and who can therefore
consider such majors in college. Again,
the changes are slow, but since our society
is now one in which the majority of women
are employed outside of the home for a
major part of their adult lives, they should
lead to much more substantial numbers
of young women laying the foundation in
high school and college for graduate work
in physics.

In the past, there has also been sub-
stantial attrition in graduate school, with
twice as many women graduate students
in physics terminating with a master’s
degree than was the case for men.7
Again, anecdotal evidence indicates that
negative peer attitudes concerning the
appropriateness of scientific careers for
women were an important factor, together
with the perception that job opport unities
were limited for doctorate-level women

Women Faculty in Physics Departments

Department Type and Rank 1971-72a 1978-79b

"Top Ten”c Percent ( number )

All Professors

0.8 ( 4)

2.7(11)

Full Professor

0.6 ( 2)

10 ( 3)

Associate Professor

1.1 ( 1)

5.8 ( 3)

Assistant Professor

0.9 < 1)

7 7 ( 5)

Otherd

2-8 ( 1)

5.0 ( 1)

PhD Granting

Number of Departments

(158)

(212)

All Professors

1.5 (74)

1.7 (88)

Full Professor

1.0 (23)

1.2(38)

Associate Professor

1.8 (24)

1.5 (22)

Assistant Professor

2.0 (27)

4.5 (28)

Other11

5.9 (17)

4.5(15)

MA Granting

Number of Departments

(133)

(123)

All Professors

2.3 (28)

2.5(27)

Full Professors

1.9 ( 7)

1.5 ( 8)

Associate Professor

2.2 ( 9)

2.9(12)

Assistant Professor

2.6 (12)

4.4 ( 7)

Other'1

4.6 ( 6)

16.2(11)

BA Granting

Number of Departments

(743)

(606)

All Professors

5.4(144)

3.9 (93,

Full Professor

5.8 (55)

3.2 (29)

Associate Professor

4.9 (33)

3.9 (35)

Assistant Professor

5.2 (56)

6.9 (39)

Other'1

9.5 (44)

11.4 (27)

All Three Types

Number of Departments

(1034)

(941)

All Professors

2.8(246)

2.5(218)

Full Professor

2.4 (85)

17(75)

Associate Professor

2.7 (66)

2.5 (69)

Assistant Professor

3.3 (95)

5.5 (74)

Other13

7.6 (67)

8.3 (53)

a. 1971-72 data from "Women in Physics", report of the Committee on Women in Physics of the American Physical Society,
Bull. Am. Phys. Soc. 17, 740 (1972).

b. 1978-79 data compiled from the "1978-79 Directory of Physics and Astronomy Faculties," American Institute of Physics
(1978). Astronomy Faculty are not included.

c. The top ten in 1970 according to the American Council on Education: Berkeley, Caltech, Chicago, Columbia, Cornell, Harvard,
Illinois, MIT, Princeton and Stanford. The same institutions were included for 1978-79 sample. There were two additional
women in the Division of Physics and Astronomy at Caltech who were designated astronomy faculty.

d. Lecturer, instructor, research professor, etc.

physicists. Bluntly, why get a PhD in
physics when you can’t get an interesting
job and it makes it harder to be married?
Other contributing factors that have been
mentioned are isolation, not being in-
cluded in the collegial interactions of the
peer group, and “invisibility” — not being
perceived as a serious student by profes-
sors. Here again, changing attitudes
concerning appropriate roles for women
and the changing views of marriage must
also have improved the general situation
in the last ten years. Furthermore, af-
firmative action, ineffective as it has been
on the whole, has created the impression
that doctoral women scientists can get
jobs. It comes then as no surprise that
more women now continue to a doc-
torate.

The third category of reasons for the
difference between the statistical patterns
for women and those for men listed at the
beginning of this section is discrimination.
Although it is generally hard to document,
there is considerable direct evidence that
discrimination has been an important
factor. Universities have had overt
policies of not accepting women graduate
students, of not hiring women faculty
even though they educated women stu-
dents, and of favoring men for promotions
and pay increases because they “needed
it more, they had a family to support.”
There is also considerable anecdotal evi-
dence of discriminatory attitudes. For
example, there is the thesis supervisor
who advised a woman student to look for
a job as a scientific editor, since such a job
would be more compatible with marriage
and a family than a position requiring her
to do research. Or the numerous profes-
sors who said that they did not want
women graduate students because they
once had a very good one who quit to raise
a family as soon as she got her degree. It
is interesting that, although I have heard
this from so many individuals that it

should be a significant statistical effect,
the evidence is quite to the contrary.
Approximately 95% of the women who
received a PhD have remained profes-
sionally active, although a substantial
number took time off or worked part time
when their children were small.7

There have also been regulations that
were de facto discriminatory, such as
nepotism rules invoked mainly against
wives. The classic example is Maria
Goeppert Mayer, who was denied a paid
scientific position for a major part of her
scientific career and did not receive a
full-time professorship until after the
publication of her Nobel prize-winning
work on the nuclear shell model.20

And finally there has been an inability
to recognize women as plausible scientists,
which certainly must have colored the
reactions of those men so affected toward
the hiring or promotion of a woman sci-
entist. An experimentalist recently
commented to me that physics depart-
ments were obviously “leaning over
backward to appoint women as assistant
professors” because in the last five years
the percentage of these appointments
that have gone to women has been about
the same as the percentage of recent
physics doctorates earned by women.
The phase “leaning over backward”
clearly reflects an attitude about the
qualifications of women in general which
can not help but influence decisions on
individuals. This perception of women
physicists is still quite widespread and is
not only held by older scientists. The
person who made this remark is a gener-
ation younger than I. Discriminatory
attitudes also frequently manifest them-
selves in an unwillingness to admit that a
woman could succeed. I have heard a
number of people say that Enrico Fermi
“gave” Maria Mayer the nuclear shell
model, or that Pierre Curie was mainly
responsible for the Nobel prize shared

with Marie Curie. The evidence supports
neither assertion. It is, of course, difficult
to assign credit when work is done jointly
by husband and wife. However, in nu-
merous articles mentioning Marie Curie
as a scientist who won a Nobel prize in
1903 jointly with her husband and An-
toine Becquerel, there is no mention that
she received a second unshared Nobel
prize in 1911 for the discovery of radium
and polonium after her husband’s death
and no mention of the fact that she was
the only person to receive two Nobel
prizes until 1962. These stories are not as
trivial as they may seem, because they
translate to “Oh, her husband (professor,
coworker, and so on) did the important
part of the work” when such attitudes are
encountered by less famous women sci-
entists. Only time can cure such atti-
tudes, as the men who hold them retire
and are replaced by others who have had
women physicists as professors and peers,
and are at ease with them.

The fourth category of reasons for the
differences between the participation of
men and women in physics stems from
conflicts between the demands of a career
and those of personal life, particularly if
these involve marriage and children, be-
cause these conflicts have in the past
generally been seen as a problem that the
wife must resolve. An interesting con-
sequence of this was observed by Lindsey
Harmon in a study of early performance
indicators, such as high-school grade
point averages and college entrance tests,
of individuals who subsequently received
doctorates. Almost without exception in
all fields the married women ranked
highest on all indicators, with single
women ranking next, followed by single
men and finally by married men. This
was a totally unexpected result for which
Harmon suggested the following expla-
nation: “When the superiority of women
over men doctorate-holders was noted in

the study of 1958 graduates, the hypoth-
esis was advanced that this was due pri-
marily to the greater hurdles the women
had to overcome to attain the doctorate
degree ... It is assumed . . . that marriage
and its attendant responsibilities is a
handicap rather than a help in further
academic attainment for the women”.21

This is true not only in the US. In the
USSR women participate in substantial
percentages in all branches of science and
technology through the first level of the
universities, but there is a steady decrease
in the percentages for higher levels of
achievement. For example, in 1970, 50%
of the junior scientific assistants, 24% of
the senior scientific assistants, 21% of the
docents (roughly postdoctoral level) and
10% of the professors were women.
Twenty-seven percent of the candidate
degrees in science (roughly PhD level),
but only 13% of the doctorate degrees in
science (a higher level) were awarded to
women.22 A number of sociologists, both
Soviet and non-Soviet, have suggested
that this is due to the fact that Soviet
women are mainly responsible for the care
of the household and children.23 Al-
though it is obvious to even the occasional
visitor that other factors such as dis-
crimination also contribute to the differ-
ences in the Soviet Union, it is clear that
the much greater difficulty of maintaining
a family in the USSR would be a crushing
burden to a research career.

In theory, evidence that marriage ad-
versely affects women’s careers could be
observed in terms of differences in rates
of publication. Experimentally, different
studies give different answers to this
question.24-25 I am personally aware of a
substantial number of women scientists
who have combined an active research
career with raising a family. However, in
numerous surveys it has been found that
in the past women scientists have fre-
quently accepted less demanding careers

because of their roles in their marriages.
They have been willing to put their hus-
band’s career first, to move to areas where
there were no or inferior job opportunities
for the wife, to assume the major share of
household labor and the responsibility for
children, and to choose teaching over re-
search because it meshed better with their
family duties. In recent years, however,
there has been a change in the attitudes
toward marriage and roles in marriage.
Many young couples are considering
having no children or, at most, one, and
many marry with an explicit under-
standing that their careers have equal
priority and that they share equal re-
sponsibility for all facets of their married
lives. It will be interesting to see the ef-
fects of these changes in the next
decade.

Returning to my list of possible causes
for the differences between men and
women physicists there remains the
Matthew effect, first so identified by
Robert Merton. In the words of the
apostle:

“For unto everyone that hath shall be
given and he shall have abundance; but
from him that hath not shall be taken
away even what he hath” [Matthew 13:
12].

In Merton’s words, the Matthew effect in
science “consists in the accruing of greater
increments of recognition for particular
scientific contributions to scientists of
considerable repute and the withholding
of such recognition from scientists who
have not yet made their mark”.26 The
existence of a scientific elite has been
discussed by sociologists, notably Joh-
nathan and Stephen Cole, Merton, and
Harriet Zuckerman, and the pattern is
clear.25'27 Those scientists who work in
leadership positions at the research uni-
versities accrue grants and students that
result in publications which are in turn
rewarded by more grants, students, and

Women Nobelists. Opposite page, Maria
Goeppert Mayer, her husband Joseph E. Mayer,
Robert d'Escourt Atkinson, Paul Ehrenfest and
Lars Onsager lounging on the lawn of the Uni-
versity of Michigan summer school in 1930. Left,
Marie Curie. Rarely is it mentioned that she re-
ceived a second Nobel Prize in 1911 for the
discovery of radium and polonium after the death
of her husband She remained the only person
to receive two Nobel Prizes until 1962. (Photos
courtesy of APS Niels Bohr Library.)

prizes in a spiral of success. On the other
hand, those who are in secondary posi-
tions or at less prestigious institutions
(categories in which women have been
heavily represented) do not receive this
type of support and are unlikely to join
the elite. Even women with tenure at
major research universities may be out-
side this circle, whose members are known
to each other and who are proposed by
one another for leadership or advisory
positions, prizes and other forms of rec-
ognition. If the women scientists are
perceived as outsiders, it is unlikely that
they will develop the contacts to become
members of the scientific old boys’ club.
I was quite distressed when an eminent
theoretical physicist said to me about five
years ago that it would take two genera-
tions before there were good women
theorists. I was unhappy at the possible
impact of this point of view, and appalled
at the apparent callous disregard of ex-
isting women theorists. But in terms of
the Matthew effect, he was correct.
These women were not part of the inner
circle, and given the small numbers at the
top universities and the slow change in the
attitudes toward woman physicists held
by people like himself it will take time for
women theorists to attain significant
representation among the elite, but
hopefully not two generations.

Unnecessary, injurious, out of place?

It must be fairly clear by now that the
adjectives in the subtitle of this article are
not as extreme as they may have seemed
initially. They have all been used many
times with respect to women physicists.
Therefore let me use them as a framework
for some comments on what the future
may hold.

Is it unnecessary that women have
equal opportunity and encouragement to
become physicists? It is both as neces-
sary and as unnecessary as is the case for
men. Depending on how you look at it,
the job outlook for the future is bleak
(prestige academic positions), or better
than most fields (physics-related posi-
tions). I think that it is safe to say that a
reasonable employment situation would
continue if the number of doctorates re-
mains approximately constant; and be-
cause the percentage of physicists who are
women is so small their participation
could increase by a factor of five to six
without increasing the number of doc-
torates if there is a corresponding con-

-

SOCIAL CONTEXT

157

tinuation in the decrease in the number of
men receiving doctorates in physics. But
why encourage this to occur? The answer
is simple. Women in this country face a
future in which most of them will work
during most of their adult lives. They
therefore deserve a society in which they
can choose employment according to their
interests and abilities, and for which they
will receive the same rewards as men.
And it can only benefit the profession to
move closer to a situation where rewards
are based on a perception of scientific
merit that concerns itself with the sub-
stance of performance, not with the ex-
ternals of sex or race.

The question of whether increased
participation by women in physics would
be injurious has two aspects. One is the
indubitable fact that, if a field or job cat-
egory has become identified as a woman’s
field, it has in the past been accorded
lower prestige and a lower salary. Since
women are reaching out into almost all
careers these days their entry into various
fields is unlikely to continue to have this
effect. The other aspect of the question
is that it has required and will continue to
require external pressures such as affir-
mative action to effect equality of op-
portunity; this is viewed by some as an
infringement of personal or institutional
prerogatives by the government and a
dilution of quality. In view of the small
increases that have been achieved by eight
years of affirmative action it is not possi-
ble to tell what the effect on quality has
been. As for the question of infringement
of prerogative, I would argue that no one
should enjoy the prerogative to choose
faculty in a manner biased by precon-
ceptions and misconceptions of women.
Affirmative action is still necessary to
prime the pump, to increase the visibility
of successful women physicists in order to
create an atmosphere where women are
accepted and rewarded for their contri-
butions in all aspects of the profession. If

some appointments are made which are
not successful, it will not be a new phe-
nomenon. Many men hired by academic
institutions have been denied promotion
and tenure in the past without any dis-
cussion of injury to the profession.

Finally, there is the question of whether
women are out of place in physics. There
is no compelling evidence that girls are
not equally endowed with the abilities
necessary to become successful physicists.
There is overwhelming evidence that the
attitudes of society and the pressures of
marriage and family have made this much
more improbable for women than for
men. A prominent physicist once re-
marked to me, “It is too bad that you were
not born a man.” And indeed, there are
very few women physicists for whom there
has not arisen some career obstacle,
whether internal or external, directly at-
tributable to their sex. But, if we are in-
deed to take seriously the ideal that par-
ticipation in physics should be based on
interest, aspiration and ability, then cer-
tainly no individual should be discour-
aged on any grounds other than these.

References

1. H. J. Mozans, Women in Science, Apple-
ton (1913); reissued by MIT, Cambridge,
Mass. (1974).

2. G. Sarton, A History of Science, Harvard
U. Cambridge, Mass. (1952).

3. L. M. Osen, Women in Mathematics, MIT,
Cambridge, Mass. (1974).

4. E. T. James, Notable American Women
1607-1950, Harvard U., Cambridge, Mass.
(1974).

5. F. Rudolph, The American College and
University, Knopf, New York (1962).

6. M. W. Rossiter, American Scientist 62, 312
(1974).

7. APS Comm. Women in Physics, Bull. Am.
Phys. Soc. II, 17, 740 (1972).

8. D. M. Gilford, P. D. Syverson, “Summary
Report [Year] Doctorate Recipients from

US Universities,” Nat. Acad, of Sci. (1972
through 1978).

9. D. M. Gilford, J. Snyder, Women and Mi-
nority PhD’s in the late 1970’s: A Data
Book. Nat. Acad, of Sci. (1977).

10. B. D. Maxfield, N. C. Ahern, A. W. Spisak,
Science, Engineering, and Humanities
Doctorates in the United States. 1977
profile, Nat. Acad, of Sci. (1978).

11. B. D. Maxfield, N. C. Ahern, A. W. Spisak,
Employment Status of PhD Scientists
and Engineers. 1973 and 1975, Nat. Acad,
of Sci. (1976).

12. M. E. Law, J. Wittels, R. Clark, P. Jor-
genson, Bull. Am. Phys. Soc. 21, 888
(1976).

13. L. Tiger, New York Times Magazine, 25
October 1970, page 35.

14. E. E. Maccoby, C. N. Jacklin, The Psy-
chology of Sex Differences, Stanford U.,
Stanford, Cal. (1974).

15. A. Kelly, Phys. Bull. 30, 108 (1979).

16. M. J. Oates, S. Williamson, Signs, 795
(Summer, 1978).

17. M. E. Tidball, V. Kistiakowsky, Science
193, 646(1976).

18. S. Tobias, Overcoming Math Anxiety,
Norton, New York (1978).

19. C. E. Max, “Opportunities for Women in
Physics,” U. California Rad. Lab. Report
UCRL-80943 (1978).

20. J. Dash, A Life of One 's Own, Harper and
Row, New York (1973).

21. L. R. Harmon, High School Ability Pat-
terns, Nat. Acad, of Sci. (1965).

22. G. F. Schilling, M. K. Hunt, “Women in
Science and Technology: US/USSR
Comparisons,” Rand Paper Series P-239,
Santa Monica, Cal. (1974).

23. W. M. Mandel, Soviet Women, Doubleday,
Garden City, N.Y. (1975).

24. J. A. Centra, Women, Men and the Doc-
torate, Educ. Testing Serv., Princeton,
N.J. (1974).

25. J. R. Cole, S. Cole, Social Stratification in
Science, U. Chicago, Chicago, 111. (1973).

26. R. K. Merton, Science 159, 56 (1968).

27. H. Zuckerman, Scientific Elite, Free Press,

New York (1978). □

SOCIAL CONTEXT

159

PHYSICS TODAY / NOVEMBER

Spencer R. Weart

Spencer R. Weart is director of
the Center for History of Physics,
American Institute of Physics,
New York.

Laser-assisted machining.

Lasers are based on old theory;
what is new is their uses, which
range from experiments in
fundamental physics to the
machining operation shown
here. Uncovering the subtle
complexities of Nature and
making use of the results is the
hallmark of modern physics.
(Courtesy General Electric
Company, Research and
Development Center)

The last

fifty years -
a revolution?

1981

In some periods great conceptual
revolutions shake the world of
physics; at other times research
seems to plod ahead within the
confines of an established frame-
work. And the structure of the
physics community must change
in a way that somehow matches
the changing style of research.
What, then, has been the form of
physics during our own lifetime,
and how has it changed? This is
a difficult, but not impossible ques-
tion. Only history can give us an
inkling of the answer.

To place ourselves here in
1981, on the fiftieth anniversary of
the American Institute of Physics,
we need to imagine how physicists
fifty years ago saw their own
place. Suppose there had been a

fiftieth anniversary of something
back in 1931 — what would those
physicists have said about their
position in time? In fact we have
a good idea of that, because peo-
ple back then wanted to orient
themselves in time just as much
as we do now, and they often re-
corded what they thought of their
situation.

Physicists in 1931 saw them-
selves at the crest of a great,
spreading wave of new knowl-
edge. They were right to think so,
considering what physicists had
done in the half-century up to
1 931 . Most striking, perhaps, was
the development of electromag-
netic theory and practice. Only in
1 888 did Hertz detect electromag-
netic waves, sealing the process

«

Modern sophistication.

People fifty years ago could
scarcely foresee the power and
insight that modern physicists
bring to the study of complex
phenomena. Sophisticated
instruments probe at the
borders between disciplines.
Shown here are an electron
microscope and the
oceanographic instrument
platform “Flip Ship. "

Computers similarly broaden
the range of theory. Here we
see the density of the
calculated fissioning state in
silicon-28 [H. and R.

Schuitheis, Phys. Rev. C 22
(1980): 1588] and melting and
vaporization at the surface of a
heated theoretical solid [F. F.
Abraham, Phys. Rev. B 23
(1981): 6145],

SOCIAL CONTEXT

161

The Physics Community — A Retrospective

by which Maxwell’s equations
came to be accepted as definitive.
It was between then and 1931 that
most homes got their dozens of
electric lights and their dozen or
so little electric motors. In 1931
the silver-haired dean of American
physicists, Robert Millikan, told the
New York Times that this was the
greatest change of the previous
couple of generations: the substi-
tution of electrical power, driven
by fossil fuels, for human muscle
power. No past time had known
such a great change, he said, and
he could not imagine that physics
could bring any change so great in
the next couple of generations.1
The revolution in communications,
symbolized by radio and tele-
phone, was also largely complet-
ed.

In the more abstract kingdom of
theory, the physicists of 1931
could look back on equally great
changes. Fifty years before, sta-
tistical mechanics had barely start-
ed, and some leading scientists
even refused to agree that atoms
existed. Then the work of Boltz-
mann, Gibbs, and many others es-
tablished the statistical atomic the-
ory beyond question, solving one
of the oldest problems of sci-
ence. This atomic view had then
been pressed forward to the dis-
covery of that most fundamental
particle, the electron. The discov-
ery of x rays and radioactivity add-
ed to the excitement: At last the
structure of matter was becoming
known.

But that was only an appetizer.
During their own careers the
physicists of 1931 had overthrown
the commonsense view of how
atoms must behave, creating the
new quantum mechanics. To many
the quantum seemed incredible,
bizarre. Yet by 1931 the quantum
view had been capped with the
Dirac theory. And the positron,
just discovered, confirmed Dirac in
a most surprising way.

And even that was not all. Ein-
stein had replaced Newtonian me-
chanics with his special theory of

relativity, and had gone on to build
a new general theory that ex-
plained gravity in a far deeper way
than before. Just as the discov-
ery of the positron had unexpect-
edly underwritten Dirac’s theory,
so the discovery of the expansion
of the universe gave an astound-
ing demonstration of the useful-
ness of Einstein’s equations.

The only word for all of this is
revolution. The physicists of 1931
were keenly aware that their gen-
eration had upset previous ways of
seeing the universe, as thoroughly
as Lenin's generation had upset
the social structure of Russia.

Said Millikan: “The discoveries
which I myself have seen since my
graduation transcend in funda-
mental importance all those which
the preceding 200 years brought
forth.”2 A revolution is a com-
plete turnabout; that well de-
scribes what had happened to the
world-view of physics in the fifty
years up to 1931.

A social revolution

Physics had known a social rev-
olution too, almost as radical as
the new theories. This was par-
ticularly true in America. Back
when Millikan and the other senior
physicists of 1931 began their
education, American physics
scarcely existed. Then came the
foundation of The American Phys-
ical Society and the Physical Re-
view, which together defined the
existence of an American physics
community. These were joined by
other institutions, such as the
American Association of Physics
Teachers, brand-new in 1931.
There were something like 3000
physicists in the United States in
1931, where fifty years earlier
there had been at best a couple of
dozen. In that year 1931 the
Physical Review, for the first time,
was cited more often in the phys-
ics literature than its chief rival, the
German Zeitschrift fur Physik.

This rise of American physics

was a world-historical change,
more significant in the long run
than the bloody useless battles of
the First World War. The leaders
of physics, when they thought
about the effects of that war,
thought particularly of how physi-
cists had proved themselves in in-
dustry. As recently as 1 900 there
had scarcely been such a thing as
an industrial physicist, but in 1931
about one-fifth of the members of
the Physical Society were in indus-
try. There was talk of forming a
society of industrial physicists —
splitting up the Physical Society.3

Along with this growth had
come an important change in the
public attitude toward physics.

Our science had always been re-
spected for its deep understanding
of nature, and also for its promise
of making life on earth easier. But
in the fifty years up to 1931 the
admiration had redoubled. The
discoveries of quantum mechanics
and relativity put physics, for the
first time, beyond the reach of the
intelligent layman. Einstein was
the first physicist ever to be re-
garded, even by intellectuals, with
the uncomprehending awe once
reserved for sorcerers. Meanwhile,
the practical value of science had
been proven in the war and in the
industrial laboratories. The physi-
cists of 1931 could look in any
magazine and find advertisements
declaring that some particular
toothpaste or refrigerator was
made better by laboratory scien-
tists. That was something new,
something revolutionary.

How confident was the public in
1931 about science? Nothing
shows it better than peoples’ de-
sire to make themselves radioac-
tive. Radium could help cancer
patients, of course, but that was
not all; many people thought that a
little radioactivity could be a
healthful stimulant. Spas in many
countries were proud to advertise
the natural radioactivity of their
waters. A 1 929 pharmacopoeia
listed no less than eighty patent
medicines based on radioactivity.

162

HISTORY OF PHYSICS

You could take radium by capsule,
tablet, compress, bath salts, lini-
ment, cream, inhalation, injection
or suppository. You could eat
mildly radioactive chocolate can-
dies, then brush your teeth with ra-
dioactive toothpaste. The manu-
facturers claimed that their
nostrums would give relief from tu-
berculosis, tumors, rickets, bald-
ness and flagging sexual powers.4

Despite all the enthusiasm for
science, the public had some
doubts. The increasing applica-
tion of physics to industry in war
and peace, and the increasing fail-
ure of most people to understand
physics, led to criticism. Physics
was said to stifle the spontaneous,
unthinking wholeness of life, to de-
stroy moral values, to reduce
workers to robots or throw them
out of work entirely.

New problems require new solu-
tions. Many leaders of physics in
1931 saw a serious need to keep
the public trust in physics. They
also needed to deal with the rise
of industrial physics, which threat-
ened to cause a schism between
industrial and academic physi-
cists. But most pressing, they had
to reorganize the finances of phys-
ics journals, for the journals were
losing money as the physics com-
munity became increasingly spe-
cialized. It was to meet all these
needs that the American Institute
of Physics was founded. The
newborn AIP had the practical
task of making publication more
economical by consolidating the
production of the various physics
journals. But it had even more im-
portant tasks, as the people who
founded it saw things: To cement
a bond between industrial and
academic physics, and to serve up
reliable information on physics to
the press and the public. With the
founding of the AIP, the structure
of American physics was put in or-
der.

When physicists of 1931 looked
ahead to our own time, they were
sure that physics would continue
to grow and spread into every field
of human activity. They said that
power would become still cheaper
and more widely used. They ex-
pected that by the 1989s we
would have widespread use of
television, transportation much
better than steamships and some
kind of industrial robots. In all this
they were quite accurate.

Physicists were less accurate
when they looked at their own sci-
ence. In 1931 the problem of the
nucleus had grown so pressing
that it seemed to tremble on the
edge of a grand solution, and
many hoped for a new revelation,
as exciting and surprising as quan-
tum mechanics or relativity. Niels
Bohr even suggested in 1931 that
the law of conservation of energy
might have to be junked. In
George Gamow’s draft for a text-
book, wherever he talked about
the internal constitution of the nu-
cleus he drew a little skull and
crossbones in the margin, to warn
the reader how uncertain the cur-
rent speculations were.5

While nuclear physicists awaited
their revelation, others worked in
another direction to undermine the
recently won achievements of
quantum mechanics. These oth-
ers were few but they were led by
the greatest of all, Einstein. The
union of electromagnetic and
gravitational theory seemed not far
off. And would that not put both
general relativity and quantum me-
chanics to rest, as mere shadows
of some far grander and deeper
unified field theory? Such were
the dreams of 1931.

Uncovering new
subtleties

Where are we now in 1981?
Are our times much like the times

of the people fifty years ago? Is
the history of physics in our life-
times much like the history that
they lived through, or are there
qualitative differences? There
can be no simple answer, for
physics is an uncommonly diverse
subject, but I can mention a few
particularly salient features.

The study of nuclear forces and
particles has not brought the new
revelation, the overthrow of quan-
tum mechanics. Instead of wholly
new laws, we have been uncover-
ing ever more layers of complex-
ity. Quite a lot has been said re-
cently, in connection with the 1980
Nobel prizes,6 about theoretical
developments, so I will touch on
some of the experimental results.
First there were the mesons, and
then a number of other particles,
particularly the strange particles —
as the name implies, quite a sur-
prise for physicists. This particle
zoo, as it was called, gradually
sorted out; the discovery of the
omega minus gave an encourag-
ing confirmation that the zoo had a
comprehensible layout. And lately
there came the experiments that
most of us would call the confir-
mation of quarks: another layer of
complexity.

Did all this add up to the sort of
revelation that physicists of 1931
had seen in their past or hoped to
achieve with nuclear physics? I
think the answer must be no — not
exactly. Certainly the appearance
of new particles has been surpris-
ing and exciting. People in 1931
really thought that with the elec-
tron and proton (and conceivably
the neutrino) they had counted up
all the fundamental particles.

That sort of thinking has been
overthrown. Yet the overthrow
was in no way comparable in
scope to the discovery of the elec-
tron or to quantum mechanics.

The idea of fundamental particles
is as useful now as it was then;

r

SOCIAL CONTEXT

they just turn out to be more nu-
merous and subtle than people ex-
pected.

I am not speaking now of the
new unified force theories. After
all, these still involve a pile of em-
pirical parameters. Historians of
the future may well say that the
year 1981 marks the center of a
slow revolution in our view of
forces and particles, but it is too
early for a historian to write about
that yet.

What has been most striking is
not the revolutionary nature of
these fundamental theories but
their continuity, their tortuous step-
wise development out of earlier
theories. In some ways it has
been less a process of inventing a
new theory, in the sense of a new
world-view, than a process of sep-
arating out the valid theories from
the almost infinite variety spread
forth by quantum mechanics.
Contrary to what many scientists
expected in 1931 — above all Ein-
stein— quantum mechanics re-
mains and is more solid than ever.

But it has not remained un-
changed. There was, of course,
confirmation that it really worked,
right down to the incredibly fine
detail revealed by the Lamb shift.
That was more than some expect-
ed. But there was also a new ap-
proach to quantum electrodynam-
ics associated with the names
Feynman, Tomonaga, Schwinger
and Dyson. In one sense this is
only a better means of calculation,
but we must beware of saying
“only” a means of calculation,
when that is all any theory comes
down to when you go into the lab-
oratory. It was not easy for many
people to swallow renormalization,
and it was not easy to swallow the
notion, so clearly pointed out by
the diagrams of particles interact-
ing, that a positron can be repre-
sented as an electron going back-
wards in time.

163

Albert Einstein, Hendrik
Antoon Lorentz and Arthur
Stanley Eddington in 1923.
These theorists pursued an
underlying unity and simplicity.
Similar work over the last half-
century has advanced less
rapidly than work in their day.
(Photograph courtesy of AIP
Niels Bohr Library.)

I

Entire attendence at 1930 meeting, and
recent single session. Growth of the
physics community changed its character.
The participants at the 1930 Washington
meeting of the American Physical Society
would have had little time to chat during
the crowded sessions of any meeting since
the 1960s. (Photographs courtesy AIP
Niels Bohr Library)

On top of these subtleties came
the discovery of parity violation.
Even more fundamental was the
violation of CP, which is to say,
the experimental proof of time
asymmetry, an even more funda-
mental reversal than the reversal
of an electron into a positron.
These discoveries surely did upset
old preconceptions. Yet again, I
will not call them revolutionary in
the sense that quantum mechan-
ics had been. No old system of
ideas was turned on its head.
Rather, people were set free to
consider a greater range of ways
the universe can behave — this
freeing-up was indeed necessary
to open the way to the new unified
force theories.

As with quantum mechanics, so
with the general theory of relativ-
ity, the years have seen not an
overthrow but a strengthening.

The unification of electromagne-
tism with gravitation— the project
on which Einstein spent half his
life — is not yet done, nor does
quantum mechanics seem any
easier to reconcile with a theory of
curved spacetime. Yet this does
not mean there has been no pro-
gress. To begin with, general rel-
ativity has passed exacting experi-
mental tests, much as quantum
mechanics did, and that is great
progress. And there have been
wonderful developments in the
theory — not new equations but
new theorems spinning out from
the old equations, each more as-
tonishing than the last.

Consider, for example, the rela-
tions among cosmology, thermo-
dynamics and relativity. It has
gradually dawned on physicists

that the direction of entropy, the
direction of time, is somehow em-
bedded in the general relativity so-
lution for the expanding universe,
in the elementary sense that
time’s arrow points the direction
away from the Big Bang. More-
over, we have learned how even
that “singular” solution of the
equations, a black hole, can have
its own time scale, a lifetime deter-
mined by statistical, indeed quan-
tum emissions.

A hundred years ago, in 1881,
there was simply Newtonian time,
a concept scarcely different from
that handed down from Aristotle, a
concept of crystalline simplicity.

By 1931 this was done away with,
replaced by relativistic time — a
new way of putting time into our
equations, an astounding revolu-
tion. Yet Einstein’s idea of time
was as easy as Newton’s, once
you got used to it, and even
simpler; that was why physicists
liked it. But what has happened
since then? Relativistic time is
still basic. But the concept has
been wonderfully enriched. Time
is reversible; time symmetry is not
even conserved; time plays fantas-
tic tricks around spacetime singu-
larities; time is tied up with all the
majestic expansion of the uni-
verse. The physicist’s conception
of time is today far more complex
than in 1931, much richer and
more subtle.

So when I say that there has
been no revolution in the last fifty
years comparable to those of the
fifty earlier years, I’m not heaping
scorn on recent progress. Phys-
ics does not always have to ad-
vance in a revolutionary way.

Sometimes it advances precisely
by coming to more complexity,
more layers, more calculations
and models, more subtlety. No
doubt the universe is character-
ized by great simplicities, not all of
them known; but the universe is
also characterized by an intricate
physical texture, which it is also
the task of the physicist to under-
stand.

Freeman Dyson makes a similar
point when he divides scientists
into “unifiers” and “diversifiers.”7
As an example of a unifier he sug-
gests Einstein, always searching
for underlying unities; a diversifier
would be someone like the great
majority of our colleagues in biol-
ogy, always studying the marvel-
ous diversity of specific creatures.

This is in fact a fundamental di-
vision in the way humans can ap-
proach the universe. Many years
ago, in the classic study of mysti-
cism, Underhill pointed out that
mystics may approach God in two
ways. They may see God as tran-
scendent, wholly other; or they
may see God as present in all
things, diverse and evolving.8 In a
similar way, the search for some
transcendent unity beneath the
surface of things was an important
root of modern science, but the
love of diversity, of particular
things in the world, was no less
important.

The two feelings could be com-
bined in one person. Galileo was
certainly a unifier, and he found
fundamental laws beneath the mo-
tions of things. But he was also a
diversifier. The old unitary theory
of his day saw the sun as a per-
fect sphere, and the planets car-

ried around the sky on perfect
crystal spheres. Galileo, peering
hour after hour through his tele-
scope, discovered the moons of
Jupiter and the sunspots, and
messed up that beautiful, clean
theory. Galileo loved change and
diversity; dirt, he said, was better
than diamonds. If the whole earth
were a perfect crystal sphere, said
Galileo, he would consider it just
“a wretched lump ... in a word,
superfluous.”9

A Broader Scope

Both unifiers and diversifies are
important in science. But there
may be times when one type of
thinking can make swifter progress
than another. And in physics of
the last fifty years, while much at-
tention has gone to the efforts of
unifiers, I think much of the finest
work has been in the direction of
diversity.

Take, for example, astrophysics.
Compared with what we know
now, the people in 1931 knew al-
most nothing. They did not even
know whether red giants are an
early stage of the evolution of
stars, or (as is the case) come lat-
er. Today, the evolution of stars
is better understood than the
transformations of a tadpole into a
frog. Then, more recently, there
was all the development of radio
astronomy. A whole new uni-
verse, the so-called violent uni-
verse, is now open to us.

Yet none of this is what I would
call revolutionary. Some of what
astronomers guessed in 1931
turned out to be wrong, but no

strongly held astronomical world-
picture was overturned. It was
not that astronomers had a wrong
idea of the radio universe or of
stellar evolution, so much as that
they admittedly did not understand
these things at all. Modern astro-
physics has not been like a revolu-
tion overturning an established
government; it has been more like
a wave of colonization that sets up
new nations in an uninhabited ter-
ritory.10

This colonization was made
possible because of the alliance of
astronomy and physics. Nuclear
physics and spectroscopy and
electronics and optics have all
been essential to the advance of
modern astronomy. Indeed, for
some time now about half of all
new astronomers have brought
their PhDs from physics. In re-
turn, physics has been enriched
beyond measure by what the as-
tronomers know.

This kind of cross-fertilization is
another aspect of what I have
been talking about: the increase
in richness and complexity that
has been the main feature of
physics for the past half century.
Astrophysics is not the only exam-
ple. Another would be geophys-
ics. The 1 930s saw a massive in-
vasion of oilfields by physicists
with gravimeters and the like.

Since then there has been a true
scientific revolution among our col-
leagues in geology, the develop-
ment of plate tectonics — the view,
stoutly resisted by many old-tim-
ers, that the continents slip about
like so many cakes of ice on a
churning ocean. While many lines
of evidence converged on this rev-

elation, not least in importance
were techniques brought in from
physics, such as measurements of
the radioactive ages and magnetic
orientations of rocks.

It was not by a fluke that phys-
ics became an indispensable part
of the tool chest of many other
sciences. The great discoveries
preceding 1931, statistical me-
chanics, radioactivity, the electron
and all, laid a firm conceptual
foundation not just for physics it-
self, but for all the sciences. It re-
mained only to apply these tools
to the thousands of old problems
that awaited them. And who
could do this better than physi-
cists?

The most exciting example of all
was molecular biology. In 1931
physicists and biologists had little
to do with one another. Then
came the discovery of artificial ra-
dioactivity. By the end of the
1930s, in laboratories around the
world — Berkeley, Paris, Copenha-
gen, Tokyo— cyclotrons or other
particle accelerators were being
built. But most of them were not
built primarily to explore the nucle-
us. These devices were funded
above all to provide artificially ra-
dioactive isotopes for biological
and medical research.

The new coalition between
physics and biology spread after
the Second World War. Erwin
Schrodinger went so far as to sug-
gest that if physicists went into bi-
ology they might discover, in those
huge complex molecules, revolu-
tionary new laws of physics. That
was a fantasy, but physicists, in-
spired by Schrodinger, gave biolo-
gists important help in deciphering

B

166

the genetic code. More impor-
tant, the analytical ways of thought
pioneered by physicists conquered
certain fields of biology. And most
important of all were the physical
techniques, especially radioactive
tracers. It is hard to say where
molecular biology would be today
without all that — certainly far be-
hind where it is now.

When physicists back in 1931
looked ahead they foresaw some-
thing of this. “Questions of life and
health,” said Arthur Holly Comp-
ton, “will probably be in the fore-
front.” And Millikan said, “It is
rather in the field of biology than
of physics that I myself look for
the big changes in the coming
century.” They predicted this be-
cause they foresaw that physics
was bound to enter and inspire bi-
ology.11

The last fifty years, then, have
revealed an ability of physics, a
surprisingly powerful ability, to help
make sense out of the most com-
plicated phenomena, even in fields
far from home. But most striking
has been the way that physics has
done this in its own central area,
the understanding of everyday
matter.

The physicists of 1931 would
certainly be gratified to see the ad-
vances that have been made in
understanding collective phenom-
ena, not only in inaccessible
places like the nucleus or a neu-
tron star, but even in ordinary mat-
ter. For example, behavior near
the critical point is understood now
in a far more satisfying way than
formerly; the unifiers have done
well here. But no field exemplifies
so clearly as solid-state physics
the urge to look into diversity and
understand it.

The band theory, the study of
point defects and their conse-
quences, the theory of supercon-
ductivity and the study of lattice vi-
brations are just part of a list that
could go on for pages. I wish I
could tell in a few words the story
of this field, because in many ways
the history of solid-state physics,
its growth into condensed-matter
physics, has been at the heart of
the history of physics over the last
fifty years. We all know of the
great applications, not only the
long-predicted televisions and ro-
bots, but also the computers, with
their little-anticipated power to help
along every field of science. But I
think many people do not realize
the fundamental interest of this

HISTORY OF PHYSICS

Brookhaven National Laboratory in 1962, as seen
from the air, looking south. Only national
governments could support science on such a scale.
(Photograph courtesy of AIP Niels Bohr Library.)

field. The condensed-matter
physicists are the ones who pro-
vide an explanation of the physical
characteristics of everyday matter:
they can literally tell us why the
things we see and handle look
and feel as they do. This is pri-
mary among the ancient, homely
tasks of physics, and it is a task
that has been largely accom-
plished in our time.

I wish, I say, that I could tell the
story of this development, but I
can’t. The story has not yet been
put together by historians. Why
has fundamental solid-state phys-
ics gotten less public attention
than many other fields? I suspect
it is because the field is obviously
not revolutionary. Once again, it
has been more a matter of people
colonizing unknown territory,
through steadfast continuous
work, rather than overturning what
was known. Cyril Stanley Smith
has written about this.12 Solid-
state physics, he feels, was held
back because of an overemphasis
on “good, clean” Newtonian
methods. Only when people ac-
cepted a messier, more approxi-
mate way of dealing with things
could solid-state physics be
done. “I rather suspect,” Smith
writes, “that solid-state physics
has in it some of the future of sci-
ence in dealing realistically, not
purely statistically, with complicat-
ed systems, and not being purely

reductionist as almost all physics
was until 1940 or so.” He calls
the history of solid-state physics
“the history of an emerging sci-
ence of buildings, not of bricks.”

I think something like that could
be said for much of the history of
physics over the past fifty years.

Certainly there are times when
revolutionary ideas are adopted—
and noboby would dare say such
times may not be here today.
However, there are also times for
diversity, for the advance of a sci-
ence of buildings, not of bricks,
and those can be exciting and im-
portant times too.

An institution
transformed

Turning now from physics as an
intellectual field to physics as a
community of people, what has
happened in the past fifty years?
Again I do not see revolutionary
changes. There has been nothing
comparable to the preceding burst
of activity that took American
physics from a nonentity to a field
with its own journals, societies and
Institute. Today as in 1931, physi-
cists are organized in the Physical
Society and others, with the Phys-
ical Review and some other jour-
nals. Today there are still a fifth
of the Physical Society members

r

WIDE WORLD PHOTOS

Research teams and equipment grew
vastly in fifty years. Carl Anderson (above)
designed by himself the device he used to
discover the positron in 1931; Samuel
Ting's team (right) fitted easily into one
corner of the apparatus they used to
discover the J/\p particle in 1974.

AIP NIELS BOHR LIBRARY

in industry, with most of the rest
employed by academic institu-
tions. Yet underneath this there
have been changes. And just as
in physics itself, the changes were
no less important for being com-
plex and subtle rather than revolu-
tionary.

For example, those people em-
ployed by academic institutions to-
day are in large measure paid by
the federal government. This is
particularly obvious for the quarter
of them who work at government-
contract laboratories, perhaps less
so for professors who indirectly
draw part of their pay from the
government’s tuition subsidies.
This dependence on federal mon-
ey would have horrified Millikan, a
sturdy free-enterpriser. Yet he
should have foreseen it, for even
in his day the United States was a
holdout, a country of privately em-
ployed physicists in a world where
the salaries of most physicists
were paid by national govern-
ments. This great change in
American physics does not seem
so revolutionary, then, when seen
in the perspective of world histo-
ry. Physics tends to be strongly
supported by the state, a fact that
has been clear in most countries
for many years.

Another change is also not sur-
prising, except in its scope: the

rise of American physics to world
dominance. In 1931 Millikan pre-
dicted that by our time, “the Unit-
ed States and Germany will prob-
ably be the world leaders in
science.” Only two years later
Hitler came to power, and the
cream of Central European scien-
tists began to make their way to
American shores. Since then, the
United States has been the loca-
tion for more important theories,
experiments and instruments than
all the rest of the world put togeth-
er. This dominance of a field of
science by one country is without
precedent in modern history.

It was government funds as
much as anything that allowed
this, promoting a great increase in
the number of physicists. Where
there were some 3000 physicists
in America in 1931, there are over
30 000 now. Any physicist in
1931 could have predicted some
such increase, simply by extrapo-
lating the exponential growth that
had already been going on for
generations. In fact, an extrapola-
tion would have indicated close to
100 000 physicists in the 1980s.
However, around 1 968 the growth
reached saturation — the maximum
number of physicists that society
was willing to support. The end of
exponential growth demanded a
number of painful readjustments,

which are still underway.

It would have been harder for
the physicists of 1931 to under-
stand what the increase in num-
bers would mean for their way of
life. The break came sometime in
the 1950s when American physi-
cists could no longer all know one
another as the people in a small
town know one another. Rela-
tionships shifted. Some obvious
indicators are the innumerable
parallel sessions at meetings, the
insuperable thickness of the Phys-
ical Review , and the need for
weighty grant applications rather
than a simple chat with your pa-
tron.

Another indicator is the rise of
team research, and the clustering
around great instruments, a way of
working that would have been
wholly alien to the physicists of
1931. Yet that is no revolution,
really, for the old-style physics still
goes on where it can. It is again a
matter of increased complexity, of
diversity, of deeper levels of un-
derstanding and organization mak-
ing it possible to break into new
territory. (Perhaps in some way the
nature of the social organization
parallels the nature of the knowl-
edge it makes available; that deep
question cannot be answered
here.)

As one indicator of the in-

168

HISTORY OF PHYSICS

Twenty-three-year-old cartoon. Close new
connections of physics with the military since World
War II altered the physics community and increased
the public's ambivalence toward science. (Drawing
by Model!; © 1958 The New Yorker Magazine, Inc.)

“ From the cyclotron of Berkeley to the labs of

We’re the lads that you can trust to keep our country strong and free.”

creased complexity of the physics
community, look at the American
Institute of Physics itself. There
has been no revolution, for it is still
the old AIP established fifty years
ago. But what a difference! In-
stead of a director and one secre-
tary operating in a free-wheeling
way out of a tiny office, AIP is to-
day an organization as diverse as
a large bank, with 400 employees
clustered around computer termi-
nals and the like. Besides its old
task of publishing journals (now
using physics-based electronics
technology, of course), it address-
es the problems jointly faced by
the various physics societies
through an array of sophisticated
mechanisms: a public affairs com-
mittee, representation in copyright
clearance organizations, a market-
ing apparatus, manpower studies,
a public information service and
even a history center. In short,

AIP and the physics community,
along with the subject of physics

itself, have become far more com-
plex and more intricately intercon-
nected with the rest of the world in
the past half century.

In this matter of connections
with the rest of the world, there is
one more thing I must talk about.
Robert Millikan and Arthur Comp-
ton would have been most sur-
prised to see it. That is the fact
that today, as through the past for-
ty years, something like a quarter
of all American physicists are em-
ployed rather directly in military re-
search. Beyond this, the armed
forces have given generous sup-
port even to research that seems
quite pure — for generals too have
grown sophisticated, and under-
stand the long-term sway of sci-
ence. Most physicists, like my-
self, have benefited at one time or
another from Department of De-
fense contracts. I think that the
physicists of 1931 would find it
overpoweringly strange that so
many scientists now work on

weapons, and I think that some,
for example Compton, would be
distressed. They believed that
the physics research of today is
the main factor in determining the
world of tomorrow. So they would
want to know what sort of a world
we have it in mind to create.

It may well be that this revolu-
tion, this infection of physics by
military problems, also has some-
thing to do with changes in public
attitudes toward our science. I do
not think there has been a com-
plete revolution here; the public is
still mostly enthusiastic about our
enterprise. Yet consider how
people think of radiation. Nobody
wants to become radioactive any
more. On the contrary, people
have become as unreasonable in
their fear of radioactivity, as they
were unreasonable in their hopes
for it fifty years ago. The change
can be dated very precisely: it
was caused by Hiroshima. Since
then, any public support for phys-
ics has had within it a certain fear-
ful reservation, and rightly so, if
you consider our situation. This is
another of those subtle changes, a
new complexity, a new wisdom I
suppose, that we must live with.

Fortunately, many physicists
themselves have responded by
taking their social responsibilities
more seriously, and dealing with
them in a more understanding and
sophisticated way. The growing
recognition that even in the ab-
stract acts we perform in our re-
search, physicists are human be-
ings living in society, is one of the
most subtle and most hopeful of
all the changes we have seen.

To answer, finally, the question I
began with, I do not think that
physics in our times has been like
the physics of fifty years ago. Our
times have been less revolution-
ary, but more diverse and pene-
trating; less welcoming to dreams
of vast revelations, but no less ex-
citing and rewarding. Of course,
this history shows us no way to
predict whether our fifty years of
development have built a platform
for another revolutionary leap, or
whether the steady process of ex-
tending and reinforcing the struc-
ture of our science will continue
for many years. But the history
does show that if we are to keep
physics vigorous, we must always
be ready for changes in our social
arrangements and even in our ap-
proach to knowledge.

SOCIAL CONTEXT

169

References

1. New York Times , 30 September 1931,
X:3. See also Millikan, Science and the
New Civilization , Scribner’s, Boston
(1930), page 73.

2. Millikan, Science and Life, Pilgrim, Bos-
ton (1924), page 68.

3. S. Weart, “The Physics Business in
America, 1919-1940: A Statistical Re-
connaissance,” pages 295-358 in Na-
than Reingold, ed., The Sciences in
The American Context: New Perspec-
tives, Smithsonian Institution, Washing-
ton, D. C. (1979).

4. Public attitudes to radioactivity will be
discussed in my book, Nuclear Fear ,
now in preparation.

5. Gamow, Constitution of Atomic Nuclei
and Radioactivity, Oxford U. P. (1931).

6. Nobel Prize lectures, published in Rev.
Mod. Phys. 30 (1980) and
elsewhere.

7. F. Dyson, “Infinite In All Directions,”
address to American Association for
Advancement of Science, Toronto,
January 1981.

8. Evelyn Underhill, Mysticism, 12th edi-
tion, Dutton (1961), pages 40-41, 99,
128, 291. See also Arthur O. Lovejoy,

The Great Chain of Being, Harvard U.
P., Cambridge, Mass. (1964), pages
83-84 and passim.

9. Quoted in Arthur Koestler, The Sleep-
walkers, Grosset & Dunlap, New York
(1963), page 474.

10. David O. Edge and Michael J. Mulkay,
Astronomy Transformed: The Emer-
gence of Radio Astronomy in Britain,
Wiley, New York (1976), pages 386-
94.

11. New York Times, 30 September 1931,
X: 3.

12. C. S. Smith to author, 31 October

1980. □

i

171

—Chapter 4
Biography

Biography is one of the favorite modes of historical
writing, so widespread that it has almost become a
genre of its own, as shown by the separate racks given to
"Biography” in paperback bookstores. Some of the articles
in this section, particularly the ones on Oppenheimer and
Urey, follow the normal historical mode of looking into just
what happened during a particular period of the protag-
onist’s life, but other articles are more impressionistic. All
of them deal with something that goes beyond history of
physics into other forms of literature: the investigation of
character.

The people described in this section were at the very top
of their profession (and so are many of the authors).
Biography is not interested in ordinary lives but in those
that touch greatness. We read biography to participate
vicariously in such extraordinary lives, and also to try to
understand how some people manage to rise above the
common. In science the matter is not only of personal
interest but of practical importance, for studies have shown
that a large fraction of the most important research has
been done by a very small fraction of all researchers.

What makes some people great scientists? The articles
here, and many other studies, show that raw intelligence is

not the only answer. Some of the people discussed, such as
Rutherford, themselves insisted that their minds were not
remarkably brilliant or subtle. What seems to have been
more important for all successful scientists is what the
Victorians called moral energy — a drive to work hard and
take chances, an indefatigable boldness, combined with
honesty at the most basic level, a common sense that does
not hesitate to identify the scientist’s own errors.

Note too that every one of the scientists memorialized in
this section showed high ability at getting on with other
people. As students they worked well under the direction of
their seniors, and when they became leaders in turn they
inspired not only hard work but admiration and even love
among their own students and their colleagues. They had
less pleasant characteristics too, sharp edges which many
of our authors have hesitated to discuss in public; none of
these scientists succeeded without being ready to fight for
what they wanted. In any case these articles imply that the
comic-book image of the scientist — an inhumane genius
cogitating solitary thoughts in a sterile white laboratory —
portrays only the kind of person who makes little
impression on history.

Contents

173

194

198

208

214

221

228

234

The two Ernests

Van Vleck and magnetism

Alfred Lee Loomis — last great amateur of science
Harold Urey and the discovery of deuterium . .

Pyotr Kapitza, octogenarian dissident

The young Oppenheimer: Letters and recollections

Maria Goeppert Mayer — two-fold pioneer
Philip Morrison — A profile

Mark L. Oliphant
Philip W. Anderson
Luis W. Alvarez
Ferdinand G. Brickwedde
Grace Marmor Spruch
Alice Kimball Smith
and Charles Weiner
Robert G. Sachs
Anne Eisenberg

■

i.

BIOGRAPHY

173

The Two Ernests — I

Some personal recollections of Ernest Rutherford and Ernest
Lawrence in the period 1927-1939. Rutherford, who dominated
the Cavendish Laboratory, gave his physicists a minimum of
equipment hut a maximum of personal interest in their re-
search. Lawrence developed the Radiation Laboratory into a
prototype facility for research with large, expensive equipment.
Both inspired others to produce and interpret nuclear reactions.

PHYSICS TODAY / SEPTEMBER-OCTOBER 1966

by Mark L. Oliphant

ox 11 January 1939 after a visit to
Berkeley, I wrote a letter to Ernest
Lawrence that contained the following
paragraph:

“I find it very difficult to thank
you for the magnificent and in-
structive time which I had in Berke-
ley. It was truly fine of you to be
so liberal of time and of thought on
my behalf. I know of no laboratory
in the world at the present time
which has so fine a spirit or so
grand a tradition of hard work.
While there 1 seemed to feel again
the spirit of the old Cavendish, and
to find in you those qualities of a
combined camaraderie and leader-
ship which endeared Rutherford to
all who worked with him. The es-
sence of the Cavendish is now in
Berkeley. I am sincere in this, and
for these reasons I shall return again
some day, and I hope very soon.”
Now, in 1965, after many subse-
quent visits to the Radiation Labora-
tory, which Lawrence created and
which is now named after him, I re-
main intrigued by both the many
similarities, and the differences, be-
tween Rutherford and Lawrence.

John Cockcroft and Ernest Walton
first observed nuclear transformations
produced by artificially accelerated par-
ticles, and [antes Chadwick discovered
the neutron, in the Cavendish Labora-

tory, Cambridge, in 1932. Lawrence
conceived the cyclotron principle in
1929, in the University of California,
Berkeley. By 1932, with his colleagues
Niels Edlefsen and M. Stanley Liv-
ingston, he had made the cyclotron a
successful instrument with which he
was able to confirm the restdts of
Cockcroft and Walton, and carry
them to much higher bombarding ener-
gies. The period between these great
discoveries and that of the fission proc-
ess by Otto Hahn and Fritz Strassmann
in 1938, was of the greatest importance
in the development of modern phys-
ics. In this article, f endeavor to set
down some recollections of that pe-
riod and of two individuals who gave
it such momentum that it changed
the whole course of physics and led,
inexorably, to the development of nu-
clear weapons and nuclear energy. No
pretense is made that this account is
complete, or that the facts presented
are in accordance with the recollections
of others who lived through those stir-
ring days. The study of the effects pro-
duced in the atomic nucleus by bom-
barding it with nuclear projectiles had
transformed knowledge of matter and
its properties. The parts played by
Rutherford and Lawrence, directly
and indirectly, will remain outstanding
contributions to that work.

Ernest Rutherford and Ernest Law-

rence. in two succeeding generations,
built around them great schools of in-
vestigation that laid the foundations
of physics as it is practiced today.
These two men, so much alike, and
yet so strangely different, were parts
of totally different worlds. Together,
their lives spanned the period of the
greatest revolution in knowledge of
the physical universe since Newton’s
time. Each was a pioneer, and each
was the descendant of pioneering
parents who chose to build a new
life in a land far removed from the
home of their ancestors. It is revealing
to review the early life of each.

Rutherford, early years

Rutherford’s grandfather, George
Rutherford, migrated from Scotland to
New Zealand in 1842. His son James,
then three years of age, grew up in

Sir Mark Oliphant,

K. I!. E„ F. R. S„
worked with Ernest
Rutherford in the
Cavendish until
1937, when he went
to the Univ. of
Birmingham. In 1950
he became professor
of particle physics
and director of the
Research School of Physical Sciences at
the Australian National University.

HISTORY OF PHYSICS

174

HOUSE, in South Island, New Zealand
where Rutherford lived as a child.

the colony and followed his father’s
trade as a wheelwright. James met
and married a widow, Caroline
Thompson, who had left England for
New Zealand with her parents, in
1855. They settled near Nelson, in
the South Island, where James Ruther-
ford had a small farm and worked as
a contractor building the railways.
Ernest Rutherford was born on 30
Aug. 1871, the second son in a large
family of twelve children. When Er-
nest was eleven years of age, the fam-
ily moved a short distance to Have-
lock, where his father established a
mill to treat the native flax of the
area, and a small sawmill. At the
primary school there, Ernest was in-
fluenced by his teacher, J. H. Rey-
nolds, who taught so well that Ernest
won a scholarship to Nelson College,
with almost full marks in the examina-
tion. He entered the College at 15
years of age, and was much helped
by one of the masters, W. S. Little-
john, a classicist who taught also
mathematics and science. Ernest had a
broad education, excelling in mathe-
matics, but winning distinctions in
Latin, French, English literature, his-
tory, physics and chemistry, and be-
coming head of the school. He was a
scholar of distinction, but played
games reasonably well and entered ful-
ly into the life of the school. A. S. Eve,
in his biography of Rutherford, quotes
a fellow student as saying, “Ruther-
ford was a boyish, frank, simple and
very likable youth, with no pre-
cocious genius, but when once he
saw his goal, he went straight to the
central point.” He took photographs
with a home-made camera, dismem-
bered clocks, made model water wheels
such as his father used to obtain pow-
er for his mills. Under the influence

of his mother and his fine teachers,
Rutherford developed a wide taste for
literature and read avidly all his life.
He became especially interested in bi-
ographies.

In 1889 he won a scholarship to
Canterbury College, Christchurch, a
component college of the University of
New Zealand. There, as one of 150
pupils in the small institution, he en-
joyed five very full years, obtaining
successively his B.A. and M.A. de-
grees, the first in Latin, English,
French, mathematics, mechanics and
physical science, and the second, at
the end of his fourth year, with a
double first in mathematics and physi-
cal science. During his fifth year,
Rutherford concentrated on Ids sci-
ence, carrying out many experiments
on the electromagnetic waves discov-
ered by Heinrich Hertz, and investi-
gating the effects of the damped oscil-
lations of the Hertzian oscillator upon
the magnetization of steel needles and
iron wires. He showed that the mag-
netization was confined to a thin,
outer layer of the metal, by dissolving
away the surface in acid.

Rutherford was able to use these
magnetic effects to detect the wireless
waves from his oscillator, and demon-
strated that these waves travelled for
considerable distances, passing through
walls on the way. He reproduced
Nikola Tesla's experiments on the
high voltages that could be produced
with a resonant transformer, and de-
veloped techniques for measuring in-
tervals of time as small as 10 microsec.
He spoke to meetings of the Science
Society on his work and on the evo-
lution of the chemical elements, and
he published two papers in the Trans-
actions of the New Zealand Institute.
He found it necessary to supplement
his scholarship by coaching students,
and went to live with a widow, Mrs.
de Renzy Newton, whose daughter
Mary he later married.

In 1895 Rutherford applied for an
1851 Scholarship, which was awarded
to a New Zealand student in alternate
years. The examiners of the 1851 Royal
Commission, in London, awarded this
to a chemist, J. C. Maclaurin, but
were impressed enough by Rutherford
to urge the award of a second scholar-
ship, which was not given. However,
Maclaurin gave up the scholarship to

accept an appointment in the civil
service; so Rutherford was offered the
award. He elected to go to the Caven-
dish Laboratory, in Cambridge, to
work under J. J. Thomson, and had
to borrow the money to pay for his
passage to England. He and John S.
Townsend, of gas-discharge fame, ar-
rived at the Cavendish Laboratory al-
most simultaneously, to become the
first of the new category of research
student recently established in the
University of Cambridge. There he
joined Trinity College and began
fresh experiments on the detection
of electromagnetic waves by use of the
effects of high-frequency currents upon
the magnetization of iron wires. He
soon established himself as a research
worker of great promise, of whom
Andrew Balfour wrote, “We’ve got
a rabbit here from the antipodes and
lie’s burrowing mighty deep.” Ruther-
ford was ambitious and anxious to
qualify for a post that would enable
him to marry Mary Newton. He
thought that the detector using very
fine magnetized steel wires surrounded
by a solenoid in which high-frequency
currents reduced the magnetization
might make his fortune. Before Gu-
glielmo Marconi, he was able to de-
tect radio waves at a distance of half
a mile.

Rutherford developed early an ex-
traordinary ability to recognize, and
concentrate upon, the puzzling prob-
lems of frontier knowledge in phys-
cis. He was never content to follow
pedestrian paths of measurement or
rounding off of investigations initiated
by others. George P. Thomson, in his
Rutherford Memorial Lecture, pointed
out that Rutherford was working in
the Cavendish Laboratory when two
completely new physical phenomena
were discovered. These were the dis-
coveries of x rays, by Wilhelm Roent-
gen, and of radioactivity, by Henri
Becquerel and each opened up hither-
to unsuspected areas of investigation
destined to change the course of phys-
ics. It is not surprising, therefore, that
when J. J. Thomson invited Ruther-
ford to join him in the investigation
of the ionization produced in gases by
x rays, Rutherford seized the oppor-
tunity to move into more exciting
fundamental studies.

Rutherford showed that the ioniz-

BIOGRAPHY

175

ing effect of x rays was due to the
production of positive and negative
ions in equal numbers and devised
ingenious methods for measuring the
velocity of drift of these ions in an
electric field. Then in 1898 he in-
vestigated the ions produced when
ultraviolet light fell on a metal plate,
showing that they were all negative
ions and that their properties were
identical with the ions produced in the
gas by x rays. Upon hearing that
the radiations discovered by Bec-
querel to be spontaneously emitted
by uranium and thorium were able
to ionize gases, Rutherford made ob-
servations of the properties of the
ions produced, and found them identi-
cal with those that he had investi-
gated previously. He showed that two
kinds of radiation were present, an
easily absorbable and strongly ionizing
component which he called “alpha
rays,” and a much more penetrating
radiation to which he gate the name
“beta rays.” He had found the field
of physics in which he was to spend
his life.

In August 1898 Rutherford was ap-
pointed to a professorship of physics
at McGill University. He had applied
for the post reluctantly, after assessing
his prospects in Cambridge, mostly be-
cause of his desire to get married,
but, having made the decision he ac-
cepted enthusiastically. Upon arrival
in Montreal he rapidly established
himself, and was soon at work on the
further studies of radioactivity that
were to establish him as the greatest
experimental physicist of his day. In
the summer of 1900, he went to New
Zealand to collect his bride, returning
to McGill in the autumn. In 1901 their
only child, a daughter, was born.

Rutherford’s subsequent work in
Montreal, Manchester, and Cambridge,
is part of the history of science, in
every textbook.

Lnu'rence, early years

Lawrence’s grandfather, Ole Lawrence,
left his home in Norway to settle in
Madison, Wisconsin, in 1840. There
he became a school teacher in a primi-
tive, pioneering community. He sent
his son, Carl, to the University of
Wisconsin, from which he graduated
in 1894. Carl followed his father’s pro-
fession as a teacher and showed that

he inherited the pioneering spirit, for
he moved farther west to South Dako-
ta as a Latin and history master.
He became superintendent of public
schools in the small community of Can-
ton, and while there, married Gunda
Jacobsen, the good-looking daughter
of Norwegian immigrants, in 1900. Er-
nest Lawrence was born to them on
8 Aug. 1901.

Ernest’s parents were good people,
in the old-fashioned sense of these
words. Although his father had a de-
gree in arts, and had taught the hu-
manities, he was not a scholar, lhe
mother, a teacher of mathematics be-
fore her marriage, became an excellent
wife and mother. She was a strict
Lutheran, mingling high principles and
loving care in the upbringing of her
two sons, Ernest and John. From his
parents Ernest acquired a strict moral
code and a belief in the inherent
decency of most human beings. Carl’s
ability as an administrator, combined
with his integrity, led to his becoming
in turn head of the Southern State
Teachers’ College in Springfield, and
then of Northern State Teachers’ Col-
lege in Aberdeen, South Dakota. So,
the family enjoyed modest means, but
not sufficient to enable the boys to
indulge in extravagances without earn-
ing money for themselv es.

Ernest grew to be a tall, gangling
youth. Unlike Rutherford, he did not
enjoy the rough and tumble of team
games like football but enjoyed ten-
nis. which he played well, if not bril-
liantly, throughout his life. His career
at high school was not outstanding,
and though he showed promise in sci-
ence, he performed indifferently in
English. He read very little, and in
later life was sarcastic about and im-
patient of his humanist colleagues, see-
ing little practical good in their work.
He was never a cultured man and
had few of the social graces so that he
made few friends among girls and did
not shine in extracurricular activities
of the school. However, he was by no
means antisocial, these traits arising
from indifference towards any activity
that did not fire his interest. He was
ambitious and worked hard and con-
sistently, so that he graduated from
high school at 16 years of age after
three, instead of the usual four years.

Durine the Iona summer vacations.

RUTHERFORD AT 21, while a student
at Canterbury College, University of
New Zealand. Photo from A. S. Eve,
Rutherford , Cambridge University Press.

LECTURING AT McGILL University,
1907, after Rutherford left Cambridge.

1

JESSE BEAMS shares a laboratory with Lawrence at Yale University, 1927, where
they developed a technique to observe the lifetimes of excited atomic states.

Lawrence worked on farms in the dis-
trict, as a salesman for aluminum
ware and in other ways earned the
money required to buy the necessities
of an American boy with a mechani-
cal turn of mind— motor cars of various
vintages, radio receiving equipment,
tools and electrical gadgets, and so on.
No doubt under the influence of the
concern for others of his parents,
he decided upon a career in medicine,
and he was sent to a small private
college, St. Olaf’s in Minnesota, to
begin his preliminary studies. He was
too young and unsettled to do well
there. After a year he moved to the
University of South Dakota. He soon
applied to the dean, Lewis E. Akely,
for permission to build and operate a
radio transmitting equipment. Akely
was much impressed with the knowl-
edge and ambition of the youth, and
persuaded him to turn to physics,
providing him with individual tuition
in the subject in order to give him a
start. After graduation in chemistry—
he had not abandoned his ambition
to do medicine— Lawrence was persuad-
ed by his close friend, Merle Tuve,
and by the offer of a fellowship, to
move to Minneapolis. There he
worked with W. F. G. Swann, an Eng-
lish immigrant who had been working
in geophysics in Washington, but who
had joined the University of Minne-
sota in order to work in more basic
physics. Leonard Loeb recalls that
Swann was not popular with his col-
leagues but that he got on extremely
well with young graduate students,

inspiring them to tlo research of qual-
ity and encouraging them with help
and discussion. Under his influence,
Lawrence abandoned his desire for a
medical career. Swann introduced him
to the exciting field of experiment
arising from development of the quan-
tum theory. His early interest in elec-
tromagnetism was stimulated and de-
veloped. He took his master’s degree
early in 1923, and later that year
moved with Swann to Chicago.

In Chicago Lawrence found himself
in a very different environment where
research was vigorously pursued by
an outstanding group of physicists.
He was stimulated greatly by contact
with Arthur Compton, at the time
completing his work on the Compton
effect. But he found himself also in a
department run on strictly European
lines, where the professor was all-
powerful and status determined the re-
lationships among members of the lab-
oratory. Neither Swann nor Lawrence
was at ease in this atmosphere, and
when Swann accepted a post at Yale,
a year later, Lawrence went with him.
In Chicago Lawrence had learned the
real meaning of research, and he threw
himself into it with complete devo-
tion. But it was at Yale that his gifts
as an experimenter, aided by his ener-
gy and enthusiasm, really flowered.
For his PhD he worked on the pho-
toelectric effect in potassium vapor,
carrying out beautiful experiments
that demonstrated clearly that he was
a physicist of high quality. Under a
National Research Council Scholar-

ship, and after appointment to an as-
sistant professorship, Lawrence con-
tinued with his researches. He made
precise observations of the ionization
potential of mercury vapor, of im-
portance in the determination of the
value of Planck’s constant h and de-
vised an elegant method of measuring
the ratio of charge to mass of the
electron. With Jesse Beams, who be-
came his firm friend, he developed a
beautiful technique for measuring very
short time intervals, which was ap-
plied to observations of the lifetimes
of excited states of atoms.

In 1928 Lawrence was offered an
associate professorship at the Univer-
sity of California, in Berkeley, having
turned down an earlier offer of an
assistant professorship. A lengthy cor-
respondence with Elmer Hall, the
chairman of the physics department,
and with Raymond Birge, who had
called on Lawrence in Yale and was
much attracted by him, has been faith-
fully recorded by Birge in the history
of the department that he is writing.
It seems that Lawrence was attracted
to California by the opportunity to
teach an advanced course and to di-
rect the work of research students, ac-
tivities reserved in Yale for more senior
members of staff. Birge pointed out
the good opportunities for rapid ad-
vancement of a good man in Berkeley,
contrasting this with the policies at
Yale, Harvard and Princeton, where it
was almost impossible to ‘‘get any-
where, after one was there, except
under very special circumstances. . . .”
Lawrence wrote to Birge saying that
some men in Yale were very “sore”
that he should even consider a posi-
tion in California to be comparable
witli one in Yale. “The Yale ego is
really amusing. The idea is too pre-
talent that Yale brings honor to a
man and that a man cannot bring
honor to Yale.”

Lawrence accepted the offer from
Berkeley, and arrived there in August
1928. He set to work at once to con-
tinue his work on the photoionization
of cesium vapor, used the techniques
which he had developed with Beams
for the measurement of short time in-
tervals in observations of the early
stages of the spark discharge, and one
of his research students, Frank Dun-
nington, developed his method for

BIOGRAPHY

177

measuring the charge-to-mass ratio of
the electron. He was not committed
to this type of investigation, however.
He felt that the current challenge in
physics was the investigation of the
atomic nucleus, rather than of the
atom as a whole. He was impressed
by the limitations of the methods of
investigation developed by Rutherford,
who bombarded nuclei with alpha par-
ticles emitted by naturally occurring
radioactive substances. Like Cockroft,
he appreciated Rutherford’s desire to
be provided with much more intense
beams of even more energetic particles
with which to probe the internal struc-
ture of nuclei.

Lawrence has recorded how, early
in 1929, he read a paper by Rolf
Wideroe on the use of high-frequency
voltages for accelerating charged par-
ticles. He recognized that it should be
possible to use a magnetic field to curl
the paths of such particles into a spiral,
and that because the Larmor time-
of-revolution in the field was inde-
pendent of the energy, they could re-
main in resonance with the voltage
across an accelerating gap. Robert
Brode has told me of a visit to him
by Lawrence the day after seeing the
article, enquiring whether the mean
free paths of ions could be made long
enough for them to suffer negligible
scattering by residual gas in their very
long spiral paths. Lawrence’s colleagues
agreed that his calculations were cor-
rect, but they were dubious whether
the method could be applied in prac-
tice.

In 1930, Edlefsen, who had com-
pleted his PhD thesis, constructed
crude models of the system and ob-
served some resonance effects. Living-
ston joined Lawrence, after Edlefsen
left that summer, and built an im-
proved model that showed resonances
corresponding with the rotation times
of molecular and atomic ions of hy-
drogen. By Christmas 1930, a 6-in mod-
el surprisingly like a modern cyclotron,
was in operation, producing hydrogen
ions with energies of 80 000 eV.

The “magnetic-resonance accelera-
tor,” as the cyclotron was first named,
had become a reality. Lawrence had
found his life’s work.

In 1932 Lawrence married Molly
Blumer, daughter of a distinguished
medical man, whom he had met while

at Yale and whom he had courted
for some years. They had six children,
two boys and four girls. He was happy
with his family, and the children en-
riched the life of both. Lawrence ap-
pears to have been a normal scientist-
father, much preoccupied with his
work, alternatively indulgent and too
strict, with his serene and capable wife
holding the balance and creating the
home.

The two compared

The similarity between the early ca-
reers of the two men is apparent. The
earliest interest of each was in radio.
However, while Rutherford abandoned
that field completely when he turned
to the study of radioactivity, the radio-
frequency problems of the cyclotron
kept alive the interest of Lawrence.
With David Sloan and Livingston he
built his own oscillators, and after the
war he developed a picture tube for
color television that is now manu-
factured by the Japanese firm, Sony.
Each moved from radio into atomic
physics, and then to the study of the
atomic nucleus. Each was single-mind-
ed, working indefatigably towards a
goal once it was chosen. Each showed
tremendous enthusiasm, which he was
able to convey to others.

Tn his early work, Lawrence showed
an insight into physics very like that
of Rutherford. Whereas Rutherford
continued throughout his life to ex-
plore in the frontiers of knowledge,
however, Lawrence chose to contrib-
ute to physics less directly. After the
discovery and successful development
of the cyclotron, Lawrence’s flair for
organization and his business ability
enabled him to build the first of the
very large laboratories in which mas-
sive and expensive equipment was de-
signed, built and used by the able
teams of men he attracted to work
with him for investigations into basic
problems in physics in which he played
little part, personally. This pattern of
research has become the modern ap-
proach all over the world. Rutherford,
on the other hand disliked large and
expensive equipment. He preferred to
remain involved, personally, in almost
all the work going on in his laboratory.
His interest and ability in administra-
tion and finance were rudimentary. He
dominated the laboratory by his sheer

greatness as a physicist and provided
for his colleagues and students only
the very minimum of equipment re-
quired for an investigation. Ruther-
ford, with his roots in the soil and the
hard, practical life of New Zealand,
bucolic in appearance, became the deep
thinker and the originator of new
physical concepts. Lawrence, brought
up in an academic atmosphere, im-
pressive and scholarly in appearance,
became the originator of new tech-
niques and of the large-scale engi-
neering and team-work approach to
discovery.

Both men were extroverts and good
“mixers” in company. Donald Cook-
sey recalls that when Lawrence entered
a room filled with great industrialists
or successful politicians, his presence
was at once noticed, and his impact
upon them was profound. Rutherford,
however, could be taken for a farmer
or shopkeeper, and it was not till he
spoke that he was noticed by those
who did not know him. Neither was
a good speaker or lecturer; yet each
influenced and inspired more col-
leagues and students than any other
of his generation. Both built great
schools of physics that became peopled
with other great men, and Nobel
prizes went naturally to members of
their laboratories. Each was most gen-
erous in giving credit to his junior
colleagues, creating thereby extraor-
dinary loyalties.

Rutherford and Lawrence were self-
confident, assertive, and at times over-
bearing, but their stature was such
that they could behave in this way
with justice, and each was quick to
express contrition if he was shown to
be wrong.

Neither Rutherford nor Lawrence
could tolerate laziness or indifference
in those who worked with them.
Rutherford said to a research student
from one of the dominions, at tea be-
fore a meeting of the Cavendish Physi-
cal Society, “You know, X, I do not
believe that you are in and at work
because your hat is hanging behind
your door!” Such a remark was far
more effective than any reprimand.
During the hectic days of the Man-
hattan Project in the war years, Law-
rence spoke to me several times of
individuals whom he felt did not share
his sense of urgency and complete

178

HISTORY OF PHYSICS

dedication to the task in hand. “I
don’t know what has gone wrong
with Y. He’s lazy and his attitude is
affecting those round him. I think
we’d better get rid of him.”

Rutherford had a great and affec-
tionate regard for Niels Bohr, who
had worked with him in Manchester.
Lawrence could not understand the
attitude of the gentle theoretician, who
had been smuggled out of Denmark
by the British and brought to Los
Alamos, where it was thought that his
genius cotdd aid the design of a nu-
clear weapon. While the task was not
completed, Lawrence could see no
sense in Bohr’s worries about how it
should be used, or his concern about
the part the devastating new weapon
coidd play in the creation of a world
without war. Great as was his admira-
tion for the man who had made a liv-
ing reality of Rutherford's nuclear
atom, he felt that Bohr was actually
holding back progress and would be
better away from the project. On his
part, Bohr found it difficult to under-
stand the complete objectivity of Law-
rence over an undertaking which cre-
ated a crisis in human affairs to which
men of science could not be indiffer-
ent.

Although wholly dedicated to the
pursuit of scientific knowledge, both
Rutherford and Lawrence delighted in
the company of men who had achieved
greatness in other spheres. Because of
their positions and reputations, they
made many contacts and a multitude
of friends among industrialists, poli-
ticians, lawyers, medical men and the
higher echelons of the civil service.
They were at home in such company
and enjoyed the good living which
many such men accepted as part of
their existence. But there was one
great difference. Rutherford enjoyed
what has been called smoking-room
humor. Although his own memory
for such stories was not good, his
great roar of booming laughter was
to be heard after dinner as he savored
the subtlety of some lewd tale. I never
heard Lawrence swear, under any cir-
cumstances, and his reaction to off-
color humor was not encouraging.

Both Lawrence and Rutherford could
be devastatingly blunt and uncom-
promising when faced with evidence
of lack of integrity, or of gullibility,

RUTHERFORD, IN 1926, visits New Zealand as Cawthron Lecturer.

LAWRENCE AT CONROLS of the 37-in. Berkeley cyclotron, about 1938.

in scientific work. 1 recollect an oc-
casion when Rutherford was asked to
advise whether the inventor of a diag-
nostic machine, which had been report-
ed upon favorably by one of the Royal
physicians, should be paid a large sum
of money for rights to use his equip-
ment. Diseases were alleged to be diag-
nosed by connecting electrodes to the
patient and observing the deflections
of meters indicating excess or defect
of various elements in the patient’s
body. The inventor explained that the
"black box” contained radioactive va-
rieties of each of the elements, where-

upon Rutherford became very angry,
pouring scorn on both the fraudulent
inventor and the gullible physicians
who believed in the efficacy of his
niachine. 1 am told that Lawrence
was invited to examine the claims of
a chemist in Berkeley who maintained
that isotopes of the chemical elements
could be detected, and their propor-
tions measured, in incredibly small
concentrations, by observation of
certain optical resonances in polarized
light, which were characteristic for each
individual isotopic mass. Looking
through the eyepiece, he could find

BIOGRAPHY

179

no evidence whatever of the maxima
and minima which were said to exist.
He burst into laughter, in a cruelly
embarrassing manner, at the self-de-
lusion of the young observer, who had
been persuaded bv the senior perpe-
trator of the hoax that there was
something to observe.

Politics

In politics, Rutherford was what
would be called nowadays, a woolly
liberal. My wife and I spent many
periods with the Rutherfords at their
country cottage, “Celyn”, in the beau-
tiful Gwynant Valley of North Wales,
and later at “Chantry Cottage” in
Wiltshire, where the walking was less
arduous. He and I often had political
arguments, which were particularly hot
at the time of the abdication of Ed-
ward VIII. I thought that no harm
would come if Edward were allowed
to marry Mrs Simpson, whereas Ruth-
erford argued that it would do irrepar-
able harm to the monarchy. His main
concern was that science should be
used properly in the development of
the economy, and on one of his rare
appearances in the House of Lords, he
advocated the establishment of a
ministry of prevision to keep the gov-
ernment informed about the advance
of science and technology and the prob-
able impact upon industrial develop-
ment. He was most generous and open-
hearted, and did all that he could to
aid the victims of Nazi persecution.
He was as suspicious of communism as
he was of extreme conservatism, but
he liked Stanley Baldwin, one of the
most conservative prime ministers Brit-
ain ever had. At heart, he was apo-
litical, but when pressed, declared
that he was a liberal.

Ernest Lawrence was both an idealist,
who cared intensely about the future
of his children and all mankind, and
a pragmatist, who saw little good in
the obsession of some of his colleagues
with the examination of social and po-
litical schemes for alleviating the lot
of humanity. Sometimes during the
war, he and I walked up or down the
hill between the Radiation Laboratory
and the campus of the university. The
downward trip usually began by his
drinking a carton of cold milk, which
I loathed, the liquid portion of which
often fertilized one of the stately euca-

lyptus trees planted on the hillside.
We would pause on the way to gaze
down over the unforgettable beauty of
San Francisco Bay. Then, and while
walking, he would tell me of his deep
concern that science be used fully to
aid the development of the human
race, and of his admiration for the
practical steps that Franklin Roosevelt
was taking to enable this to happen
in the United States. He would out-
line what he could see ahead in the
application of physical knowledge in
communications, and the productivity
of industry and agriculture. He would
express his conviction that knowledge
of matter and radiation would trans-
form the biological sciences and pro-
vide tools for medicine that would
alleviate, cure and prevent disease. He
felt that this was a task for mankind,
and not only for America, and he was
anxious to help create a world situa-
tion in which all knowledge could be
shared by all men. In a practical way
he did this whole-heartedly, helping
us all, wherever we were, to build
cyclotrons, by providing freely draw-
ings, lull details, and even his thoughts
about improvements upon what had
been built in Berkeley. Of course he
could not escape entirely the atmo-
sphere of the times, and after the end
of the war, he veered somewhat to-
wards a more restricted and less gen-
erous view of the part that his great
country should play in maintaining
the peace and assisting other nations.
But this was true only of his politics,
and his deep commitment to the de-
fense of America. In his science, he
remained the same open-hearted be-
liever in openness and in the value
of exchange of knowledge and of in-
formation in the removal of interna-
tional misunderstandings.

However, Lawrence was genuinely
apolitical. He had inherited liberal
democratic leanings from his parents,
but he could not become excited about
political issues. For instance, he was
quite unaffected by the “loyalty oath,”
which the university imposed upon
members of its staff, and which caused
great dissension among some of them.
Although unable to appreciate the
strong objections of many of his col-
leagues to what he regarded as a trivial
obligation imposed by those who gen-
erously supported his laboratory, never-

theless, he fought hard for them as
individuals.

Advice on cyclotrons

It is interesting here to recall that
the first inquiry Lawrence received
from anyone about the possibility of
construction of a cyclotron elsewhere,
was from Frederic Joliot, of Paris. On
14 June 1932, he wrote from the Lab-
oratoire Curie, saying that he had read
with great interest Lawrence’s publica-
tion on the production of ions with
high velocity. “Votre travail me parait
remarquable, et les Etudes que l’on
peut faire avec de tels rayons sont
dun grand interet.” [Your work seems
remarkable to me, and the studies that
can be made with such rays are very
interesting.] He would like to build
an apparatus of a similar type, and
to do it rapidly. To this end, he re-
quested two reprints of the article,
and any details of construction of the
“points les plus delicats” [the most
delicate points]. On 20 Aug. Law-
rence replied, apologizing for the de-
lay, and told Joliot that he might be
able to obtain a magnet made for a
Poulson arc radio transmitter, similar
to one that Lawrence had obtained
in the United States, which he under-
stood was being dismantled at Bor-
deaux.

The generous attitude of Lawrence
towards others desiring to build cyclo-
trons of their own is well illustrated
by the following extract from a
letter to Kenneth Bainbridge, dated
6 Feb. 1935:

“I have just received a letter from
Professor [George] Pegram at Co-
lumbia, saying that they want to
embark upon the construction of a
cyclotron provided that I have no
objections. I am writing him that,
rather than having objections I am
more than delighted that they are
planning to build a cyclotron. The
cyclotron to my mind is by far the
best ion accelerator for nearly all
nuclear work, and it would give me
a great deal of pleasure if many
laboratories would build them.”

On 27 Nov. 1935 Lawrence wrote to
Chadwick, congratulating him on the
award of a Nobel Prize, and offering
to give him every help in building a
magnetic-resonance accelerator in Liv-
erpool. He said that the Cavendish

180

HISTORY OF PHYSICS

must miss Chadwick greatly, but that
this was compensated by the fact that
he would build in Liverpool another
great center of nuclear physics. Chad-
wick replied that he felt rather lucky
to get a Nobel Prize and thanked Law-
rence for his offer to help to build
“your magnetic-resonance accelerator,
which ranks with the expansion cham-
ber as the most beautiful piece of ap-
paratus I know." In letters about, the
construction of cyclotrons by others,
Lawrence always emphasized that, con-
trary to the ideas of many, the cyclo-
tron was not a difficult piece of equip-
ment to get into operation.

The word “cyclotron” did not ap-
pear in any publication from the Ra-
diation Laboratory till 1935, in a paper
by Lawrence, Edwin M. McMillan and
Robert Thornton,1 where the follow-
ing footnote is inserted:

“Since we shall have many occa-
sions in the future to refer to this
apparatus, we feel that it should
have a name. The term ‘magnetic-
resonance accelerator' is suggest-
ed. . . . The word ‘cyclotron,’ of
obvious derivation, has come to be
used as a sort of laboratory slang
for the magnetic device.”

Running their laboratories

The Cavendish Laboratory, under
Rutherford and his predecessors, was
always short of money. Rutherford had
no flair and no inclination for raising
funds. Only under extreme pressure,
first from the ebullient Peter Kapitza,
and later from Cockcroft and me, was
he prepared to fight hard for money
for large or complex equipment. He
never sought riches and died a com-
paratively poor man. Lawrence, on the
other hand, had shrewd business sense
and was adept at raising funds for
the work of his laboratory. Apart
from his early interest in medicine,
he realized early the medical possi-
bilities of the radiations produced by
the cyclotron, and did not hesitate
to use these in his search for funds.
In 1935 he wrote to Bohr:

“In addition to the nuclear in-
vestigations, we are carrying on in-
vestigations of the biological effects
of the neutrons and various radio-
active substances and are finding
interesting things in this direction.
I must confess that one reason we

have undertaken this biological work
is that we thereby have been able to
get financial support for all of the
work in the laboratory. As you well
know, it is so much easier to get
funds for medical research.”
Similarly, after the war, he made full
use of the wartime achievements of
the Radiation Laboratory in raising the
support required for the very large ex-
pansion of its activities. However, it
was his concern for the defense of his
country and his belief that it was un-
wise to confine the development of
nuclear weapons to Los Alamos, which
led him to establish a branch of the
laboratory devoted to this work at
Li vermore.

Lawrence’s phenomenal success in
raising money for his laboratory was
undoubtedly due to his able handling
of executives in both industry and gov-
ernment instrumentalities. His direct
approach, his self-confidence, the qual-
ity and high achievement of his col-
leagues, and the great momentum of
the researchers under his direction bred
confidence in those from whom the
money came. His judgment was good,
both of men and of the projects they
wished to undertake, and he showed a
rare ability to utilize to the full the di-
verse skills and experience of the vari-
ous members of his staff. He became the
prototype of the director of the large
modern laboratory, the costs of which
rose to undreamt of magnitude, his
managerial skill resulting in dividends
of important scientific knowledge fully
justifying the expenditure. But in
achieving this, he had to give up per-
sonal participation in research. His
influence on the laboratory programs
remained profound, and his enthusi-
asm radiated into every corner of the
institution. William Brobeck, who
joined the Radiation Laboratory in
1936 as an engineer, recalls that Law-
rence took an animated part in all dis-
cussions of technique and showed an
extraordinary ability to see a piece of
equipment as a whole, avoiding be-
coming bogged down in detail. Law-
rence was a regular visitor to each
section of the laboratory until illness
caused him to appear very seldom out-
side his office.

Rutherford’s method of running a
laboratory was in striking contrast to
that of Lawrence. He was not much

interested in the apparatus for its own
sake, believing that techniques grew
from the demands of the experiment.
Like Lawrence, he advocated a simple,
preliminary approach, a sort of skir-
mish into the territory to be explored,
followed by refinement if the recon-
noiter showed promise. He would roam
round the laboratory, discussing results
and the physical knowledge they re-
vealed, rather than apparatus. His
stimulus was enormous, and his in-
fluence direct. A glance at any list of
publications from the Cavendish Lab-
oratory, or from the laboratories in
McGill or Manchester in his periods
there, reveals how deep was his influ-
ence on the researches carried out.
Lawrence worked to give others the
opportunity to achieve important re-
sults; Rutherford was so great a physi-
cist that almost every member of his
laboratory found himself working upon
some problem that Rutherford had sug-
gested, or that arose directly from
Rutherford’s own work. This domi-
nance was not imposed upon his col-
leagues and students. They often be-
gan work along lines of their own
choosing, but rapidly found that the
instinct of Rutherford’s genius was a
surer guide to interesting and im-
portant results.

Both Rutherford and Lawrence gave
coherence to laboratories inhabited
by workers of differing temperaments
and varying abilities. Under their in-
fluence, each gave of his best; all re-
joiced in the outstanding achievement
of one of their number, and each felt
himself to be part of the whole, shar-
ing its triumphs and its vicissitudes.

Seventh Solvay Congress

Although Lawrence had made a very
rapid tour of Europe with his friend
Beams in the summer of 1927, he and
Rutherford did not meet till 1933. In
that year, the Seventh Solvay Con-
ference, held in Brussels from 22 to
29 Oct., was devoted to nuclear phys-
ics, and, naturally, Lawrence was in-
vited to attend. He was eager to go,
since this would give him the oppor-
tunity to meet the principal workers
in his field. Those taking part
included:

From Cavendish Laboratory:

Ernest Rutherford

James Chadwick

BIOGRAPHY

181

John Cockcroft
Patrick Blackett
Paul Dirac
Cecil Ellis
Rudolf Peierls
Ernest Walton

From Institut du Radium, Paris:
Marie Curie
Irene Joliot-Curie
Frederic Joliot
M. S. Rosenblum

From the Physical Institute, Leipzig:
Werner Heisenberg
Peter Debye
From elsewhere:

Neils Bohr (Institute of Theoreti-
cal Physics, Copenhagen)

Albert Einstein (then living in Bel-
gium)

Erwin Schrodinger (Physical Insti-
tute, University of Berlin)
Wolfgang Pauli (Physical Institute,
Zurich)

Louis de Broglie (France)

Marcel de Broglie (France)

Enrico Fermi (Physical Institute,
University of Rome)

George Gamow (Institute of Mathe-
matical Physics, Leningrad)
Abraham Joffe (University of Phys-
ics and Mechanics, Leningrad)
Walther Bothe (Physical Institute,
University of Heidelberg)

Lise Meitner (Kaiser Wilhelm In-
stitute, Berlin)

Francis Perrin (Institute of Chem-
istry and Physics, Paris)

Leon Rosenfeld (Institute of Phys-
ics, University of Liege)

H. A. Kramers (Institute of Phys-
ics, University of Utrecht)

Nevill Mott (University of Bristol)
Ernest Lawrence, the only American
invited, naturally was greatly pleased
to find himself among this group of
eminent physicists who, together, rep-
resented almost all that was then
known, from experimental and theo-
retical investigation, of the atomic nu-
cleus. His invitation from the Presi-
dent, Paul Langevin, asked him to
participate in “l’examen de questions
relatives a la constitution de la ma-
tiere” [the examination of questions
relative to the constitution of matter],
and reports were to be read by Ruther-
ford, Chadwick, Bohr, Heisenberg, Ga-
mow, Cockcroft, and M and Mme
Joliot. It was clearly to be an exciting
meeting, as it was only a year earlier

that the neutron had been discovered,
and transmutation of nuclei by arti-
fically accelerated beams of charged
particles had been achieved.

In a letter to Langevin, dated 4 Oct.
1933, written after he had read the
papers that had been circulated to
those invited, Lawrence stated that he
wanted particularly to make some rath-
er extensive observations on Cock-
croft’s report, and that he might wish
to comment on papers by Chadwick,
Joliot, and possibly Gamow. He was
able to obtain funds to meet the costs
of his trip, but owing to his commit-
ments in Berkeley, he could stay in
Europe for only a very limited period.

At this time, Lawrence and his co-
workers had used the cyclotron to con-
firm the results of Cockcroft and Wal-
ton on the disintegration of lithium by
proton bombardment, and had extend-
ed their observations on this and other
transformations to higher energies.
Lawrence had eagerly availed himself
of the opportunity offered by the suc-
cess of Gilbert N. Lewis, at Berkeley, in
producing almost pure samples of
heavy water, and had accelerated the
nuclei of the new hydrogen isotope in
the cyclotron. His team observed an
enormous emission of protons and
neutrons from every target that was
bombarded, and this similarity of re-
sults, irrespective of target material,
had led Lawrence to put forward the
hypothesis that the nucleus of heavy
hydrogen, called the “deuton” by
Lewis, was unstable, breaking up in
nuclear collisions into a proton and
neutron. Meanwhile, Lewis had pre-
sented samples of heavy water to many
investigators, including Rutherford,
and we had been making observations
in the Cavendish Laboratory that were
not in accord with Lawrence’s view
that the deuton was unstable.

Lawrence went to the Solvay Con-
ference prepared to defend his hy-
pothesis and to back the cyclotron
as the type of accelerator most versatile
for experimental work in nuclear
physics. The marginal notes made by
him on the copies of the reports pre-
sented, give interesting information
about his attitudes. Some of these
are vigorous, as the large cross over
Cockcroft’s assertions that “only small
currents are possible” from the cyclo-
tron, and when Cockcroft restated this

WATSON DAVIS. SCIENCE SERVICE

CYCLOTRON MODEL is held by Law-
rence in 1930, year after conception.

later, he wrote, “Not true,” boldly in
the margin. In several places he com-
plained that the deuton-breakup hy-
pothesis received no mention, and it
becomes dear that he did not appreci-
ate fully the calculations of neutron
mass given by Chadwick, or the observa-
tions of Cockcroft, and of Rutherford
and me, which were not in accord with
his idea. He showed particular interest
in those observations reported by the
Joliots on gamma rays produced from
atoms bombarded by alpha particles,
both those collisions that result in cap-
ture of the alpha particle, and those
in which a nucleus is excited, without
actual capture.

Lawrence’s meticulous care to give
credit to his colleagures for their part
in the work in his laboratory is evi-
dent from his insistence upon the addi-
tion of their names— Malcolm Hender-
son, Milton White, Sloan, Lewis and
Livingston— wherever Cockcroft's paper
mentioned only Lawrence.

Chadwick recalls, in a letter to me,
that Rutherford was much impressed
by the vigorous young Lawrence, and
remarked to Chadwick, “He is just like
I was at his age.”

Lawrence paid a brief visit to the

182

HISTORY OF PHYSICS

Cavendish Laboratory after the Solvay
Conference, and it was then that I
met him. We had a vigorous discus-
sion, with Lawrence sticking firmly to
his concept of an unstable deuton.
When he had gone, Rutherford, said,
“He’s a brash young man, but he’ll
learn!”

Cooksey tells me that he met Law-
rence at the boat in New York on his
return to America. Lawrence was bub-
bling over with enthusiasm for all that
he had seen and learned. He was par-
ticularly enthusiastic about the great
power of the neutron as an agent for
disintegrating nuclei, and expressed
the view that, before long, these would
make possible a self-propagating reac-
tion, and hence the practical release
of energy from nuclei. A truly pro-
phetic remark.

Deuton instability

After his return from the Solvay Con-
ference, Lawrence wrote to Cockcroft
informing him that, with Livingston
and Henderson, he would concentrate
upon the origin of the protons, with a
range in air of about 18 cm, which
were emitted from all targets bom-
barded with demons. Firstly, they
would try to clear up the uncertainty
about contamination of the targets,
and if this did not turn out to be the
source of the particles, they would
“continue the experiments to shed
further light on the origin of the 18
cm protons.” He reported also that,
on his way back, he had visited Wash-
ington, where Tuve had a beam of
protons with an energy of 1.5 MeV
from his Van de Graaff accelerator.

“I persuaded Tuve to investigate
the origin of the 18 cm protons
and the hypothesis of the disinte-
gration of the deuton right away.
I want to get the matter cleared up
as soon as possible and it will be a
great help if Tuve, with his inde-
pendent set-up, will investigate the
problem.”

He wrote also to Gamow on 4 Dec.
1933, saying that he had been paying
particular attention to the hypothesis
of the disintegration of the deuton,
using clean targets and carefully puri-
fied materials. “However, we find that
the yield of protons and neutrons pro-
duced by the bombarding deutons is
quite independent of our endeavors

to clean the targets.” They found that
2.8-MeV deutons produced disintegra-
tion protons in the same proportions
as observed at 1.2 MeV. On 28 Dec.
1933 he wrote again to Gamow:

“The experimental evidence that
the deuton disintegrates is growing.
Lately, we have observed the emis-
sion of long range protons (up to
about 20 cms) resulting from the
bombardment by protons of targets
containing heavy hydrogen. Though
perhaps the matter cannot be re-
garded as entirely settled yet . . .
certainly it must be admitted that
the evidence is preponderantly in
favor of the hypothesis of the ener-
getic instability of the deuton.”
Cockcroft, in a letter to Lawrence
of 21 Dec. 1933, reported further work
on the long range protons produced
by bombardment with deutons from
lithium, carbon and boron, and noted
that while iron gave a small yield of
protons, none were observed from cop-
per, gold or copper oxide.

“We have so far not worked be-
yond 600 kV, and it may well be
that some groups appear at higher
voltages. I feel myself, however, that
the evidence so far is against your
interpretation of the break up of
H2.”

Lawrence replied on 12 Jan. 1934:

“It seems to me that you are hardly
justified in feeling that the evidence
obtained by you so far is against
the interpretation of the break-up of
the deuton, since you have not
worked at voltages above 600 kV
... it seemed pretty evident from
our first preliminary observations
that the yield of the group of pro-
tons which we ascribe to deuton dis-
integration is in all cases very small
below eight or nine hundred thou-
sand volts. Despite your greater
intensities, on the basis of our ob-
servations we would hardly expect
that you would observe the disinte-
gration of the deuton at the voltage
you have been using. ... I hope that
you will soon raise your voltage to
eight or nine hundred thousand.
Meanwhile I have written Tuve your
results and asked him to look into
the matter, as I understand he is
able to work now above a million
volts. I am anxious that the hypothe-
sis of deuton disintegration will be

settled to everyone’s satisfaction, and
to that end it seems essential that
independent experiments be carried
out in another laboratory.”

Cockcroft wrote again on 28 Feb.
1934:

“We have been working steadily
on the question of disintegrations
by heavy hydrogen. In addition to
the results on lithium I reported to
you in my last letter, we find three
groups of protons from boron. . . .

We have been investigating copper,
copper oxide, iron, iron oxide, tung-
sten and silver, with stronger heavy
hydrogen, and we find from all of
these we get three groups of par-
ticles of identically the same range.

The first is an alpha particle group
having a maximum range of 3.5 cm,
the second is a proton group of
about 7 cm, and the third is a pro-
ton group of about 13 cm. This
latter group is the one which you
ascribe to the break up of the deu-
ton. It seems in the first place clear
that these three groups cannot all
be due to this break up, and we
therefore feel strongly that the alpha
particle group and the 7 cm proton
group are at any rate due to an
impurity which is probably oxygen.

We are not yet certain about the
13 cm group, but are carrying out
experiments with white hot tung-
sten targets which I hope may finally 2
dispose of this possibility. We can
observe all these groups at voltages
as low as 200,000, and the voltage
variation shows the standard Gam-
ow tail to the curve. . . .

“I feel, however, that we have
still very good justification for re-
fusing to commit ourselves to your
hypothesis of the deuton break up
until further experimental work has
been carried out.”

To this typewritten letter, Cockcroft
added the following handwritten post-
script:

“We have now found that on boil-
ing in caustic and cleaning thorough-
ly the 1 3 cm group is reduced by a
factor 10; on heating to 2,600 by a
further factor. The 2.5 and 7 cm
groups disappear on heating and re-
appear on oxidation and seem due
to oxygen. . . . Oliphant is getting
queer results with H2 + H2.”

Lawrence replied on 14 March 1934,

BIOGRAPHY

183

agreeing that Cockcroft’s observation
that boiling tungsten in caustic re-
duces the 13-cm group by a factor 10
showed clearly that this is due to a
contamination.

“I think it is quite possible that
the effects we observed when bom-
barding targets of heavy hydrogen
with hydrogen molecular beams were
due, as [C. C.] Lauritsen sug-

gested, to an increase in deuton con-
tamination resulting from partial de-
composition of the targets. I cannot
understand my stupidity in not rec-
ognizing this possibility when the
experiments were in progress. Need-
less to say, I feel there is now little
evidence in support of the hypothesis
of deuton instability. . . .

“Rather than continuing with
preliminary and exploratory experi-
ments at higher voltages, we have de-
cided to embark on careful investiga-
tions of the nuclear effects brought to
light and we shall make as precise
and trustworthy measurements as we
can. These recent experiences have
impressed upon us forcibly the fact
that much of our work has been
of too preliminary character to be
of value. I regret very much that
the question of deuton instability
involved you in so much work, and
I want to thank you very much for
stepping in and clearing the matter
up so effectively and so promptly.”
Lawrence and his colleagues were
relatively new to nuclear physics, and
it is not at all surprising that they made
mistakes in interpretation of a com-
plex phenomenon. It was characteris-
tic of the young Lawrence that he held
tenaciously to his concept of deuton
instability, but that when presented
with definite evidence that it was
wrong, he immediately set to work
to change the approach of his team
to its experiments in such a way as
to avoid similar pitfalls in the future.

Deuton stable after all
Meanwhile, the explanation of the ori-
gin of the proton group that had led
Lawrence astray had been found in the
Cavendish Laboratory. On 13 March
1934, Rutherford wrote to Lawrence:

“I have to thank you for the very
interesting letter you sent me some
time ago giving an account of your
work. The whole subject is certainly

in an interesting stage of develop-
ment and reminds me very much
of my early ‘radioactivity’ days be-
fore the theory of transformations
cleared things up.

“I think you have heard from
Cockcroft about some of our obser-
vations the last few months. Oli-
phant and I have been particularly
interested in the bombardment of
D with D ions, and I am enclosing
a note from Oliphant giving an ac-
count of our results. I personally be-
lieve that there can be little doubt
of the reaction in which the hydro-
gen isotope of mass 3 is produced,
for the evidence from all sides is in
accord with it. The evidence for the
helium isotope of mass 3 is of course
at present somewhat uncertain but
it looks to me not unlikely.

“You will see that Oliphant like
myself is inclined to believe that the
proton group which you observe for
so many elements arises from the
reaction I have mentioned. We
have made a large number of obser-
vations with beryllium and other ele-
ments but the results are not easy
of interpretation. We think the in-
formation we have found about the
D-D reaction will be helpful in dis-
entangling the data. As you no doubt
appreciate, it takes a lot of work
to make a reasonably complete analy-
sis of the groups of particles from
any element and then it has to be
done all over again with the other
compounds to try and fix the origin
of the groups. There is an enormous
amount of work that will have to be
done with the lighter elements to
be sure we are on firm ground.

“You will have seen about Cock-
croft's results due to the bombard-
ment of carbon by protons. This no
doubt produces the radio-nitrogen
of the Joliots but we can obtain
quite strong sources of positrons by
this method. I heard that Lauritsen
or yourself had observed similar ef-
fects with I) bombardment. The
whole subject is opening up in fine
style. You will also have seen that
Oliphant and Co have separated the
lithium isotopes and confirmed the
tentative conclusions we put forward
before.” My note went as follows:

“You may have heard of the ex-
periments which we have carried out

during the last week or two on the
effects observed when heavy hydro-
gen is used to bombard heavy hy-
drogen. As I believe these are in-
timately related to your own work,
I should like to tell you what we
have found.”

The letter went on to give details of
die results, and of their interpretation
as due to two competing reactions,
the first leading to the production of
hydrogen of mass 3 and a proton, with
ranges of 1.6 cm and 14.3 cm respec-
tively, and the second to helium of
mass 3 and a neutron.

“We suggest, very tentatively, that
your results may be explained as
due to the bombardment of films
of D and of D compounds. Our re-
sults with C, Be, etc., could all be
accounted for by the presence of
less than one monomolecular layer
of D ”

On 4 June 1934 Lawrence replied
to my note, saying that the late answer
was due to his desire to be able to
send some news of interest.

“Your experiments on diplons, to-
gether with Cockcroft and Walton’s
recent work, have certainly cleared
things up in beautiful fashion. There
can no longer be any doubt that
our observations which we ascribed
to diplon break-up, are in fact the
results of reactions of diplons with
each other.”

He ended his letter with a reference
to Cockcroft’s contention, in his Sol-
vay Conference paper, that the cyclo-
tron gave only small currents:

“Dr. Cockcroft might be interested
to know also that we are gradually
increasing our currents of high ve-
locity ions, and that now we are
working regularly with more than a
microampere of either 3 MV diplons
or 1.6 MV protons and several mi-
croamperes of 3 MV hydrogen mole-
cule ions."

Lawrence had already replied to
Rutherford’s letter on 10 May 1934,
saying:

“I want to thank you for your
very much appreciated letter. Every-
one here was delighted to learn of
the extraordinarily interesting exper-
iments you have been doing on the
reactions of D-ions with each other
(perhaps I should say diplons. I
do appreciate the force of your argu-

184

HISTORY OF PHYSICS

merits in support of diplon,* but
all of us here have become quite
accustomed to deuton and it would
be some effort to change).

“It is difficult for me to under-
stand how we could have failed to de-
tect the effect of diplons on each
other. We did notice about twice as
many long range protons from the
heavy hydrogen target under bom-
bardment by diplons, but the differ-
ence between the targets was much
greater under proton bombardment.
The fact that the calcium hydroxide
targets decompose readily may in
some way account for our observa-
tions. Professor Lewis has prepared
some ammonium chloride targets and
we shall investigate the matter soon.

“The manuscript of Cockcroft and
Walton’s admirable paper has just
arrived. There can hardly be any
doubt any longer that most of the
effects which we ascribe to disintegra-
tion of diplons are in fact due
largely to a general contamination
of heavy hydrogen in our apparatus.
I certainly appreciate the manner
in which this complexity of nuclear
phenomena already brought to
light makes it clear that it is easy
to fall into error, and that a good
deal of cautious work must be done
for trustworthy conclusions.

“Fermi’s observation of radio-ac-
tivity induced by neutron bombard-
ment is a case in point. When we
bombard various targets with three
million volt deutons, large num-
bers of neutrons are always pro-
duced, which among other things
produce the types of radio-activity
discovered by Fermi. On receiving
Fermi’s reprint announcing the ef-
fect, we looked for it and found
that it was no small effect at all. For

* The evident confusion in nomenclature
arose in this way. G. N. Lewis had proposed
the name “deuton” for the nucleus of the
atom of heavy hydrogen. Rutherford ob-
jected strongly to this, feeling that it would
inevitably lead to confusion with neutron,
especially in the spoken word. After discus-
sion with his classical colleagues, he pro-
posed the name “diplon,” for the nucleus,
and ‘diplogen’ for the atom, terms derived
from Greek, and analogous to proton and
hydrogen. The dual nomenclature was given
up eventually, and the compromise “deu-
teron” and “deuterium” was accepted. It
was said by one cynic that Ernest Ruther-
ford was happy when his initials were in-
serted into deuton!

example, we found that a piece of
silver placed outside of the vacuum
chamber about three centimeters
from a beryllium target bombarded
by a half micro-ampere of three mil-
lion volt deutons became in the
course of several minutes radio-ac-
tive enough to give more than a
thousand counts per minute when
the silver piece was placed near a
Geiger counter. We are now study-
ing this type of radio-activity in-
duced in various substances and will
not return to the effects produced
by diplon and proton bombardment
until we understand pretty well the
neutron effects.

“Dr. [Franz] Kurie has been pho-
tographing with the Wilson cham-
ber the recoil nuclei and disintegra-
tions in oxygen produced by neu-
trons from beryllium bombarded by
deutons. Although the Wilson
chamber is about twenty inches
from the neutron source and there-
fore subtends a rather small solid
angle, the neutron intensity is suffi-
ciently great to give him something
like five or ten recoil oxygen nuclei
in each picture and about one dis-
integration fork per ten pictures.
Most of the disintegrations appear to
result in C13 and an alpha-particle,
but Kurie has a dozen or so which
seem to involve the emission of a
proton and therefore the formation
of N16. But these conclusions are
highly tentative. At the moment
Kurie is busy making measurements
on his photographs.

“We have sent off for publica-
tion a manuscript on the transmuta-
tion of fluorine by proton bom-
bardment and I am enclosing the
essential curves of the experimental
results. As far as we can determine,
the alpha-particles from fluorine
have a range of between six and
seven centimeters, depending on the
energy of the bombarding proton.
These results support the possibility
suggested in your paper that the
4.1 cm alpha-particles observed by
you are due to boron.

“Dr. McMillan has been studying
gamma radiation from various sub-
stances and finds among other things
that fluorine emits under proton
bombardment, a five million volt
monochromatic gamma radiation of

considerable intensity. Some day
perhaps a short range group of
alpha particles from fluorine will be
found to account for this gamma ra-
diation.

“But possibly the most interest-
ing result that McMillan has found
about this radiation is its absorp-
tion coefficient. He finds that the
absorption per electron of the five
million volt gamma radiation varies
approximately linearly with atomic
number, reaching a value for lead
double that for oxygen. In other
words, nuclear absorption (pair pro-
duction presumably) is so great that
in going from two and a half to
five million volts the absorption co-
efficient in lead does not decrease
a great deal.

“I am glad to hear that you are
very well. You need not have told
me that you are kept very busy in
the laboratory, but I was very glad
to hear that the government has giv-
en you a substantial grant of money
for research and that you are re-
sponsible for its disbursement. Also
your comparison of your early radio-
activity days with the present is very
much appreciated. I remember in
the course of my graduate studies
what a ‘kick’ I got out of reading of
the early work on radio-activity, but
I did not even hope at that time
that I would have the opportunity
to work in a similarly interesting
new field of investigation. . . .

"Please tell Dr. Oliphant that I
appreciated his letter very much and
that I will be writing him directly
before long.”

Rutherford’s brash young man
learned very quickly, as Rutherford
predicted he would. From that time
onward, the contributions made to
nuclear physics in the Radiation Lab-
oratory were above reproach and of
rapidly increasing importance, as the
energy and intensity of beams avail-
able from the cyclotron increased. □

( This is the first of two articles on
Ernest Rutherford and Ernest Law-
rence. The second xvill appear in the
next issue.)

Reference

1. E. L. Lawrence, E. M. McMillan, R. L.
Thornton, Phys. Rev. 48, 493 (1935).

BIOGRAPHY

185

The Two Ernests — II

Sir Mark continues his personal recollections of Ernest Ruther-
ford and Ernest Lawrence. By 1935 precise mass determinations
with nuclear reactions were being made at Cavendish. In the
following years Rutherford was arranging for new facilities at
the laboratory. Meanwhile Lawrence began to use the cyclotron
for medical research, learned to extract a beam from the accel-
erator and found a lot of unexpected radiation. Two years after
Rutherford’s death, the discovery of fission opened a new era.

PHYSICS TODAY / SEPTEMBER-OCTOBER 1966

by Mark L. Oliphant

Both ernest rutherford and Ernest
Lawrence led great laboratories and
inspired the physicists who worked in
them. Rutherford was personally in-
volved in almost all of the work at
the Cavendish Laboratory, dominating
the laboratory by his sheer greatness
as a physicist and providing for his
colleagues only the barest minimum of
equipment. Lawrence, on the other
hand, created at the Radiation Labora-
tory, the first of the very large labora-
tories in which massive and expensive
equipment was designed, built and
used for investigations into basic prob-
lems in physics in which he played
little part, personally. After the dis-
covery and successful development of
the cyclotron at his laboratory,
Lawrence enthusiastically offered his
assistance in the construction of cyclo-
trons at laboratories elsewhere.

The two men did not meet until the
Seventh Solvay Congress, October 1933.
At the meeting, Lawrence defended
his hypothesis that the “deuton” (deu-
teron) was unstable, breaking up in
nuclear collisions into a proton and
neutron. By May of the following year,
however, Lawrence was convinced by

experiments in the Cavendish Labora-
tory that what he had actually observed
were reactions of deuterons with deu-
terons. From that time onward, the
contributions of Lawrence’s laboratory
were above reproach and of rapidly
increasing importance as the energy
and intensity of the beams available
from the cyclotron increased.

Accurate mass measurements

One of the early results of more ac-
curate observations of the energies re-
leased in nuclear reactions involving
dre light elements was realization that
the relative masses of the atoms, as giv-
en by the mass spectrograph, were not
sufficiently reliable to give consistent
agreement. In the Cavendish Labora-
tory, we naturally used the mass de-
terminations made there by Francis
W. Aston, whose improved mass spec-
trometer was then in operation. We
came to the conclusion that there was
an appreciable error in Aston’s value
for the mass ratio of hydrogen to
helium, a basic determination upon
which many of his other mass values
depended. Aston was a touchy person
and reacted with characteristic violence

to the suggestion that there were sys-
tematic errors in his list of isotopic
masses. On 4 May 1935, Rutherford
wrote to Lawrence:

“You will no doubt have heard
from Cockcroft and others about
what is going on here. We have
given a complete account of our
beryllium results in the P.R.S.
[. Proceedings of the Royal Society\
which appears this month, and you
will see that we have put forward
a scheme of masses to fit in— prac-
tically along the same lines that
[Hans] Bethe has independently sug-
gested in your country. At first,
Aston took a high line about the ac-
curacy of his results, and the impos-
sibility of any serious error between
helium and oxygen, but when I told

Sir Mark was assistant director of re-
search at Cavendish until 1937, when he
became director of the physics depart-
ment at Univ. of Birmingham. In 1950 he
became director of the Research School
of Physical Sciences, Australian National
University, Canberra. He served for three
years as president of the Australian
Academy of Sciences.

186

HISTORY OF PHYSICS

KEY FIGURES in development and early use of the 60-in. Crocker cyclotron stand
beside the machine during construction. Only the magnet yoke and the coils have
been completed. Left to right: Luis Alvarez, William Coolidge (who was visiting),
William Brobeck, Donald Cooksey, Edwin McMillan and Ernest Lawrence.

him that if he did not get to work,
I was going to put forward the cor-
rect mass scheme, he rapidly started
in, and found that he had dropped
one or two bricks of reasonable mag-
nitude! I am not quite sure he is
right yet, but no doubt he may
amend his results later. As a matter
of fact, it is obviously very difficult
for mass-spectrographic methods to
give the same accuracy as from trans-
formations when we are sure of the
reaction.”

In his reply, Lawrence wrote:

“Your very much appreciated let-
ter was forwarded to me in New
Haven, Connecticut, late in May:
I was in the East about two months,
engaged in my annual task of raising
money for the support of our work
in the radiation laboratory. I rather
expected considerable difficulty in
raising needed funds this year, and
indeed was rather worried that we
might have to restrict our work a
great deal, but fortunately matters
turned out otherwise. In this country

medical research receives generous
support, and it was the possible
medical applications of the artificial
radioactive substances and neutron
radiation that made it possible for
me to obtain adequate financial
support. We are now able to pro-
duce several millicuries activity of
radiosodium. We are devoting a
good deal of attention to the further
development of the magnetic reso-
nance accelerator for considerably
larger currents and also higher volt-
ages. It is reasonable to expect that
it will not be very long before we
will be producing ten times as much
radioactive substance as at present.
However, according to the medical
people, at the present time we can
provide enough radiosodium for be-
ginning clinical investigations, and
we have agreed to begin supplying
the University Hospital here early
this fall.

“We have lately been making vari-
ous tests of the performance of our
apparatus with a view to the con-

struction of an improved design.
Perhaps the most interesting result
is that the focusing action of the
electric and magnetic fields is so
nearly perfect that we can get just
as large current of deuterons at 4.5
MV as at 2.5 MV. At the present
time the apparatus delivers several
microamperes of deuterons having
a range of 16.7 centimeters (about
4.5 MV) . We have bombarded
several substances, using these ener-
getic deuterons, and it appears that
almost the whole periodic table can
be activated, the type of nuclear re-
action involved being that in which
the neutron of the deuteron is cap-
tured by the bombarded nucleus.
We have found that gold can be ac-
tivated in this way, a result which
is very surprising. We shall do a
good deal more work yet on these
things before we can have confi-
dence in the experimental results
and theoretical interpretations.

“We were all very much surprised
to hear that Chadwick is leaving
you to be professor at Liverpool.
I suppose it is a promotion for
him, but I am sure that if I were
he I would be very loathe to leave
you and the Cavendish Laboratory.”

Cyclotrons for medical research
This letter mentions again Lawrence’s
readiness to develop the medical ap-
plications of the cyclotron and its
products in order to obtain the funds
required for the work of his labora-
tory. However, his interest in pos-
sible medical applications was not only
financial. His early ambition to be-
come a doctor and the fact that his
younger brother. John, had qualified
in- medicine and had become an in-
structor at Yale Medical School had
kept his genuine interest in the heal-
ing art. In the summer of 1935, John,
who had broken his leg, went to Cali-
fornia to stay with Ernest while he
recuperated. He did some experiments
while there, with the aid of Paul
Aebersold, a young colleague of Ernest.
They exposed rats to neutrons and
gamma rays from the cyclotron. On
13 Aug. 1935 Lawrence wrote a letter
to Rutherford that I quote in full:
“Dear Professor Rutherford:

“I am very, very grateful to you
for the photograph of yourself which

BIOGRAPHY

187

I shall always treasure very highly.
In asking Cockcroft to get a photo-
graph of yourself for me and ask
you to autograph it, I had in mind
that he could purchase one in a
bookstore and perhaps persuade you
to write your signature on it. I ap-
preciate very much your kindness
in sending me the portrait.

“Work is going along quite satis-
factorily in our laboratory, although
at the moment we are bothered
with cathode ray punctures of the
insulators of the magnetic resonance
accelerator, the result of increasing
the voltage and current output. My
brother, who is on the faculty of the
Yale Medical School, is vacationing
here, and I persuaded him to under-
take a preliminary investigation of
the biological effect of neutrons. He
has been exposing rats to neutrons
for periods of time from ten min-
utes to three hours, and has been
observing the changes produced in
the blood of the rats. The first rat
was exposed for a period of three
hours, and as a result died, and sub-
sequent experiments indicate that
neutron rays are considerably more
lethal biologically than x rays. The
immediate result is that we are tak-
ing rather greater precautions in the
matter of exposing ourselves in the
course of our work in the laboratory.

“I am very glad to hear that you
are well, and again I want to thank
you ever so much for your picture.

“With best wishes and highest
personal esteem, I am

Respectfully yours,”
John tells me that in fact the rat
died of suffocation, being too com-
pletely confined! However, an im-
portant result was that much more
stringent precautions against neutron
and gamma radiation were then in-
stituted in the Radiation Laboratory.
From then till 1937, John Lawrence
visited Berkeley regularly, at intervals
of about three months, taking with
him biological experiments to be car-
ried out with the aid of the cyclotron.
In 1937 he moved to Berkeley perma-
nently to take charge of the medfcal
work with a 60-in. cyclotron provided
through the generosity of Crocker.
Direct treatment of patients with
the neutron beam from the cyclo-
tron began in 1938, in collaboration

with Robert Stone of the University
of California Medical School in San
Francisco. Lawrence had encouraged
Sloan to design, and get into opera-
tion, an x-ray equipment for about
1 MV, using a resonant transformer
in a vacuum, and Stone was using
this in the hospital. The mother of
Ernest and John was treated for a
malignant growth with this equip-
ment by Stone in 1937, and the treat-
ment was so successful that it rein-
forced the faith of the brothers in the
possibility of developing still more ef-
fective uses of radiation in the treat-
ment of cancer.

New equipment at Cavendish
A letter from Rutherford to Lawrence,
of 22 Feb. 1936, contains the following
passages:

“I was delighted to get your letter
and to hear how your work is go-
ing on. I congratulate you on your
success with your apparatus in get-
ting high voltages and intense
beams. The neutron photographs
you sent me were certainly very
impressive, and 1 can roughly esti-
mate the strength of your artificial
source of neutrons in terms of ra-
dium emanation.

“1 was exceedingly interested to
hear also that you [this work was
done by John Livingood, under
Lawrence’s general direction] have
been successful in producing ra-
dium E from bismuth— a great tri-
umph for the new apparatus. I have
a personal interest in this artificial
product; for I do not know whether
you know that I worked out the
changes radium D-E-F long ago in
Montreal, and showed that as the
P rays decayed an a-ray product
grew. The apparatus I used is now
preserved in the Physical Labora-
tory in McGill. I shall be interested
to hear the details of your experi-
ments and how much radium E you
manage to produce.

“I note what you say about the
present stage of your apparatus. At
present we are very busy transferring
the apparatus from the Royal So-
ciety Mond Laboratory, and getting
duplicates, and keeping the
cryogenic work going as usual. We
do not intend to get a duplicate of
the big generator for producing

strong magnetic fields, but have in
view instead the installation of a
large magnet for general purposes,
and also probably for use as a cyclo-
tron. We have not had time as yet
to go into the matter, but I think
probably Cockcroft will be writing
to you soon to see whether you can
give him any information of the
best design of magnet to be used
for the latter purpose.

“At present we are just beginning
the new building for our high ten-
sion D.C. plant, and we hope
with luck to reach 2 million volts
positive and negative, and possibly
higher, but no doubt we will find
plenty of trouble before it is in
working operation. We shall, of
course, build up the component
parts of the apparatus ourselves so
as to keep down the expense.

“Aston will shortly be publishing
the new values of the masses of the
light elements obtained with his im-
proved spectrograph, and these new
values fit in very satisfactorily with
transformation data, so that dif-
ficulty is removed. I have also heard
from several sources that Bainbridge
has also done very much the same
thing with his new spectrograph,
and it will be interesting to see
how far these two independent sets
of measurements agree. It will be
an ultimate test of the accuracy of
these two systems.”

The reference to the Royal Society
Mond Laboratory concerns equipment
that had been provided for the work
of Peter Kapitza, the Russian engineer-
physicist who had joined the Caven-
dish Laboratory in 1921. He was in
the habit of visiting Russia during
the summer to see his old mother.
In 1935 the Soviet government re-
fused to allow him to return to Cam-
bridge, but offered to buy his equip-
ment from the university in order
that he might continue his researches
in Russia. With the able help of
Cockcroft and others, Rutherford
proved himself a better man of busi-
ness than expected, and negotiated a
good price for the equipment. Mean-
while, Rutherford’s resistance to the
idea of as complex a piece of ap-
paratus as a cyclotron in the Caven-
dish Laboratory had been worn down,
and he was willing to devote part of

188

HISTORY OF PHYSICS

the sum received from Russia to the
acquisition of a large magnet which
could be used, inter alia, for a
cyclotron.

The reply by Lawrence was char-
acteristic of his generosity towards all
who wished to build a cyclotron:

“Thank you ever so much for
your good letter. I should have
known that you were responsible
for the radium D-E-F, but I must
confess that 1 didn’t. As regards
the yields of radium E by bombard-
ing bismuth with five-million-volt
deuterons, I must say dtat they are
quite small. If 1 remember correctly,
several hours bombardment with
several microamperes gives, after a
few weeks, something like thirty al-
pha-particles count per minute when
the bismuth target is placed near
the ionization chamber of the linear
amplifier. Measurements on the
range distribution of the alpha
particles from the bismuth indicate
that the transmutation function is
exceedingly steep (for nearly all of
the alpha particles have very near
the full polonium alpha-particle
range) . It is probable, therefore, that
at six million volts, which is the volt-
age we are now using, the radium
E and polonium yield should be
very much greater; and doubtless
in the near future Dr. Livingood
will continue experiments at this
higher voltage.

“We have recently made some
alterations of the cyclotron which
have made it possible to withdraw
the beam completely from the
vacuum chamber through a thin
platinum window out into the air,
and I assure you that we have got
quite a thrill out of seeing the
beam of six-million-volt deuterons
making a blue streak through the
air for a distance of more than
twenty-eight centimeters. Our pur-
pose in bringing the beam out and
away from the cyclotron chamber
is twofold: partly to make it con-
venient to carry on scattering ex-
periments, and partly to bring the
beam to a target at a considerable
distance from the vacuum chamber
in order to get rid of the annoying
neutron background produced by
the circulating ions in the chamber
striking various parts of the ac-

celerating system. With this latest
improvement in the design of the
cyclotron, I think now we have an
apparatus which closely approxi-
mates one’s desires.

“I believe in my last letter I men-
tioned that we have been carrying
on experiments on the biological
action of neutron rays. During the
past two months such biological
matters have taken a good share of
my attention, because I feel that
such matters, as well as nuclear
physics, are of great importance.
My brother, Dr. John H. Lawrence
of the medical faculty of Yale Uni-
versity, has been out here studying
the effects of neutrons on a certain
malignant tumor called 'mouse sar-
coma 180.’ He has compared the
lethal effect of neutrons and x ravs
on the tumor and on healthy mice
and has very impressive evidence
that this malignant tumor is rela-
tively much more sensitive to neu-
tron radiation than to x-radiation.
If this is generally true for malig-
nant tumors, we have here a very
important possibility for cancer
therapy. I am sure that it will not
be long before neutrons will be
used in the treatment of human
cancer. . . .

“I was interested to hear that you
are beginning the new building for
your two-million volt D.C. plant
and that you are undertaking the
construction of a large magnet.

“I received the letter from Cock-
croft and in die next few days
will be sending him detailed infor-
mation.

“Several days ago I received an
invitation to attend the meeting in
September of the British Associa-
tion for the Advancement of Sci-
ence and I have written a tentative
acceptance and I can arrange to be
away from the laboratory at that
time. I should like very much to
come to England to spend two
weeks. In the event that you should
decide to build a cyclotron, it is
possible that I could be helpful
by going over in detail with you
matters of design.”

Unfortunately, the design of the
cyclotron for the Cavendish Labora-
tory, and its brother for Chadwick,
in Liverpool, did not follow the lines

JOHN LAWRENCE who used cyclotron
for medical research, with Ernest, 1927.

ERNEST RUTHERFORD, by Birley.

1

developed in Berkeley. It was entrusted
to a large electrical engineering firm,
with no previous experience, while
funds were too restricted to enable
the magnets to be as large as was
desirable. Much trouble was experi-
enced with them, and they never per-
formed as efficiently as the virtual copy
of the 60-in. Crocker cyclotron built
by us in Birmingham. However, they
did useful work, and established the
technique in Britain.

Biology and beam extraction

Lawrence wrote to Rutherford on 24
Nov. 1936:

“I had intended writing you some
time ago regarding Dr. R. [Ryokichi]
Sagane, who has been with us the
past year and desired to spend this
year in the Cavendish Laboratory. I
am afraid that he has arrived, and
therefore words in his behalf now
are a bit late. However, I should
like to say that we liked Sagane very
much; he proved to be a self-
reliant and competent experimenter
and a congenial personality. I do
hope that you will find him an
agreeable person to have as a visitor
in the Laboratory, for I know that
he is very anxious to be with you
and will profit a great deal by such
a sojourn.

“All of us here are very busy
with a number of things. In addi-
tion to the nuclear work, we are
devoting a lot of attention to bi-
ological problems, as I feel that
there is important work to be done
in this direction as well as in nu-
clear physics. We are supplying vari-
ous artificial radioactive substances
to the chemists for investigations
of chemical problems and to biolo-
gists, particularly physiologists, for
use as tracers in biological proc-
esses. I do hope that in this way
we shall be able to contribute to
the elucidation or some biological
questions. We are also investigating
quite extensively the biological ef-
fects produced by neutrons. I think
we can say pretty definitely now
that neutrons do not parallel x rays
in their biological action. Studies of
the comparative effects of x rays
and neutrons will doubtless shed
light on the mechanisms whereby
ionization produces effects in bi-

NEWS OF HIS NOBEL PRIZE brings joy to Ernest Lawrence, 9 November 1939.

ological systems, and of course also
there are the possibilities of effec-
tive medical therapy with neutrons.

“In some preliminary experiments
on a mouse sarcoma, we got indica-
tions that neutrons had a greater
selective action in killing this tumor
than x rays. Under separate cover
I am sending you a reprint of this
work. This fall, similar experiments
have been carried out upon a mouse
mammary carcinoma with similar in-
dications. In these more recent ex-
periments, many more tumors and
mice were irradiated with neutrons
and x rays than in the first experi-
ments on the sarcoma, and the new
data also indicate a greater selective
action of the neutrons on tumor
tissue. It seems to me quite probable
that neutrons will prove to be valu-
able in the treatment of cancer.

“We are this year undertaking
the establishment of a new labora-
tory, which might be called a labora-
tory of medical physics. The or-
ganization and planning of the new
laboratory is taking a good share
of my time this year, but of course
I am glad to do it, although I re-
gret I cannot spend full days in the
laboratory. Friends of the Univer-
sity have given funds for a new
building and equipment, and I hope
that by late next fall, experimental
work in the new building will get
under way. The architects have prac-
tically finished the building plans
and we are engaged in designing
the new cyclotron. Many of us arc

having pleasure in planning the new
apparatus; although doubtless we
are deluding ourselves into thinking
that the new outfit will be all that
a good cyclotron should be.

“For certain experiments in prog-
ress we recently further modified
our present cyclotron to bring the
beam entirely out of the magnetic
field, and we are finding the new
arrangement one of great conven-
ience for many experiments. I am
enclosing a photograph of six
microamperes of six million volt
deuterons emerging into the air
through a platinum window at the
end of a tube six feet long. The
beam is quite parallel and can be
brought out considerably farther if
so desired without undue loss of in-
tensity.

“I have heard from several sources
that you are very well and very
busy— and in view of the latter, I
can hardly expect a letter from
you, although, needless to say, I
should be greatly delighted if you
should find time to write a few
lines.

“Professor and Mrs. Bohr are
coming to Berkeley in March and
we all are looking forward to their
visit. I wish it were possible to
persuade you to visit America also.”
Rutherford replied with characteris-
tic enthusiasm for Lawrence’s success:

“I got your letter a few days ago,
and was very interested to hear of
your latest developments in getting
a beam of fast particles well out-

190

HISTORY OF PHYSICS

side the chamber. I congratulate
you on your success in this difficult
task, and I gather you are hopeful
to get even stronger beams in this
way. The photograph you have sent
me is a beautiful one, and I would
be very grateful if you would al-
low me to reproduce it in a lecture
I am just publishing called ‘Mod-
ern Alchemy,’ which is an expan-
sion of the Sidgwick Memorial Lec-
ture I gave in Cambridge a few
weeks ago. Unless I hear from you
to the contrary, I will assume that
you agree to this.

“Dr. Sagane visited us this term
and he then decided to go for a
short tour to Germany and Copen-
hagen, and is returning here in the
New Year to begin some work. He
seems a pleasant fellow, but he
writes to me that he is finding a
difficulty in seeing some of the Ger-
man laboratories, as it is necessary
to get a special permit from the
Government to do so. This state
of affairs in Nazi-land is rather
amusing, and when some of our
men from the Cavendish wished to
visit Berlin to see Debye’s labora-
tory, he wrote to Cockcroft that
official permission would have to be
granted by the Government before
he could admit them!

“As to our own work, we are go-
ing ahead as usual. The new High
Tension Laboratory is nearly com-
pleted and we hope to get a D.C.
potential of 2 million volts going.
We are also making arrangements
to run one of your cyclotrons in
due course.

“We celebrated J. J. Thomson’s
80th birthday on December 18th by
giving him a dinner and presenta-
tion in Trinity and also an ad-
dress with signatures from many of
the Cavendsh people. He is still
very alert intellectually, and he
was much moved by our little
homely address.

“I wish you good luck in the de-
velopment of your new laboratory
and success in your experiments.”

Cyclotron radiations

It was on 11 Feb. 1937 that Law-
rence wrote again to Rutherford:

“I greatly appreciate your very
interesting letter received some time

ago. I know that you are extreme-
ly busy and it is very kind of you
to write at such length.

“Your account of the state of af-
fairs in Germany is almost unbe-
lievable. One would think with
such a scientific tradition the Ger-
man people could not adopt such
an absurd course of action in sci-
entific affairs.

“The dinner to J.J. Thomson
must have been a very nice oc-
casion. It is certainly fine that he
has such vigor at his ripe old age.

“I am glad to hear that your
new high tension laboratory is
coming along nicely and that you
are also constructing a cyclotron.
As I have written Cockcroft, if we
can be of assistance in any way we
should be only too glad. I have
just heard that he is coming over
for some lectures at Harvard and
I have written him a letter invit-
ing him to come out to see us.
I do hope it will be possible for
him to do so. I think it is possi-
ble that he might be saved some
unnecessary beginning troubles by
spending a few days in our labora-
tory operating our cyclotron. Also,
in a month or so we shall have
our new cyclotron chamber for the
present magnet practically com-
pleted in the shop. This new out-
fit has quite a few improvements
which Cockcroft would probably
want to consider in his design.

“During the past few weeks we
have been bombarding with 1 1
million volt alpha particles, study-
ing the radioactivities produced. In
addition to those already reported
we have been findng many new
activities, especially on up the peri-
odic table. Also we have been mak-
ing some absorption measurements
of the radiation from the cyclotron
and find that there is a very pene-
trating component. We do not
know what it is yet, but the indi-
cations are that the penetrating
radiation consists simply of very en-
ergetic neutrons. A 7 inch thick-
ness of lead does not cut it to half.
According to Oppenheimer theo-
retical considerations indicate that
the mean free paths of neutrons
vary as their energy. Hence it may
be that, the 14 MV neutrons from

Be -f- 5 MV D2 have mean free
paths of more than 50 cms— some-
thing like the penetration of the
radiation observed. We are continu-
ing with the experiments with the
endeavor to get the experimental
facts as clear-cut and definite as
possible, and I am sure when this
is done we shall understand what
is going on. Under separate cover
I am sending you several reprints.”
He followed this with a further let-
ter of 24 Feb., having received some
reprints of lectures given by Ruther-
ford:

“Thank you very much for the
reprints of the lectures, which I
have already read with much pleas-
ure and profit. The history that
you tell about is certainly absorb-
ing. Your discussion of the essen-
tial role played by the development
of new methods and techniques in
the advance of science appealed to
me very much, as I have always
held similar views, and of course
your mention of the cyclotron in
this connection was to me the high-
est compliment. Your lectures, which
I regard as models for us younger
men, have a quality in common with
your great experimental works, that
is to say, they go to the heart of
the matter and bring out the es-
sential points with beautiful sim-
plicity. . . .

“We have been pursuing the in-
vestigation of the radiations from
the cyclotron, and have pretty well
satisfied ourselves that there is noth-
ing extraordinary about the radia-
tions excepting that it is an ex-
tremely difficult matter to screen
out all the neutrons and the gam-
ma rays from any particular region.
We have now quite a lot of water
around most of the cyclotron, but
in spite of that Professor Lewis in
the Chemistry building next door
is not able to carry on his experi-
ments with his sources of neutrons
consisting of a mixture of beryl-
lium with 200 milligrams of radium,
and we find that at a distance of
300 feet from the cyclotron the mix-
ture of neutrons and gamma rays
from the cyclotron produce an
easily detectable ionization. We are
now planning to have the cyclo-
tron in the new laboratory in a

BIOGRAPHY

191

MARK OLIPHANT AND ERNEST LAWRENCE stand before 184-in. cyclotron, 1941.

basement room rather than at
ground level in order to cut down
the amount of radiation getting out
into surrounding laboratories. I am
afraid that you will find your new
cyclotron something of a nuisance
in this regard also.”

It is clear that these two enthusi-
astic men were developing a consider-
able understanding and respect for
one another. Lawrence absorbed more
than he realized of the spirit of the
father of nuclear physics, and he
was able to pass this on to others.
The center of gravity of the study
of the nucleus was already moving
across the Atlantic to the United
States, a move which was to become
almost complete by the end of the
second world war. Rutherford was to
write only once more, in reply to the
following invitation from Lawrence:

Invitation to Charter Day

"l have just been talking with
the President of the University, who
has asked me to write you in-
formally as to whether there would
be any possibility that you might
be willing to come over here to
give a Charter Day address next
March or a year later.

‘‘Charter Day here is regarded
as a very important occasion and
the speaker at the exercise is al-
ways someone of great distinction.
President [Robert] Sproul is aware
that you may be very reluctant to
come, but is most anxious to per-
suade you to do so, since he ap-
preciates your eminence, not only
with respect to your scientific con-
tributions but also with respect to
your general scientific statesman-
ship and world wide good influence.
I do hope you will entertain
thoughts of coming over, as quite
aside from the Charter Day exer-
cises, all of us in the laboratory
would gain so much from your
visit, even though it were very
brief. Needless to say we would do
everything we could to make your
stay with us pleasant.

“The President is anxious to know
whether there is a possibility that
you will come, and so if it is not
too much trouble, I should appre-
ciate a note from you at your early
convenience. In case you should

consider coming, it would be help-
ful if you would give me some
informal indication of a suitable
financial arrangement which I could
transmit to President Sproul, as I
know it is customary to provide
a proper honorarium. . . .

“We enjoyed very much Cockcroft’s
visit, brief though it was. I need not
describe here what we did when he
was with us, as doubtless he has
given you a complete report. . . .

“Hoping to hear from you soon
and again hoping that you will actu-
ally entertain thoughts of coming
over next March, and with highest
personal esteem, I am

Respectfully yours,”
Rutherford answered:

“I have just received your letter,
asking me whether I could visit
California next March, in order to
be present at your Charter Day
Exercises.

“Please convey my thanks to your
President for his very kind sugges-
tion and invitation. I write, how-
ever, to let you know at once that
there is no possibility of a visit next
year, as I have already arranged

SKETCH of Ernest Rutherford in 1928.

192

HISTORY OF PHYSICS

to go to India in November and
preside over a joint meeting of the
British Assocation and the Indian
Association of Science, in January,
1938. I shall not return until Febru-
ary, and I shall find great arrears of
work to attend to. At this stage, I
cannot make any promises about
the following year. I have so many
calls on my time, that it is difficult
for me to make arrangements too
far ahead. At the same time, I great-
ly appreciate the very kind invita-
tion of the University and yourself.
I should personally like to have the
opportunity of visiting California
again, and in particular of seeing
something of the work of your
laboratory. Cockcroft told me about
his visit, and how kind you had
been in helping him.

“We are now preparing the foun-
dations for the cyclotron, which we
hope will be ready for transmis-
sion to Cambridge in July.

“I am glad you were interested
in the little book and the lectures
I sent you.

With best wishes,

Yours sincerely,”

Lawrence was naturally disappointed
that Rutherford could not accept the
invitation to Berkeley, but wrote say-
ing that he was glad that the possi-
bility of a visit in the followng year
was not ruled out.

Rutherford had looked forward
with keen anticipation to the meet-
ing in India. He believed implicitly
in the British Commonwealth, and his
political liberalism led to his welcom-
ing the development of responsible
self-government in India. He had had
many Indian students and had known
well that remarkable mathematical
genius, Srinivasa Ramanujan, also a
Fellow of Trinity College, who had
died so young, leaving behind a series
of intuitive mathematical theorems
that intrigued the world of mathe-
matics for the succeeding generation.
He spent much time in preparing his
presidential address for the occasion.
This address contains two passages that
are significant in the present context:

“It is imperative that the univer-
sities of India should be in a posi-
tion not only to give sound theo-
retical and practical instruction in
the various branches of science but,

what is more difficult, to select
from the main body of scientific
students those who are to be trained
in the methods of research. It is
from this relatively small group that
we may expect to obtain the future
leaders of research both for the
universities and for the general re-
search organisations. . . . This is a
case where quality is more impor-
tant than quantity, for experience
has shown that the progress of sci-
ence depends in no small degree on
the emergence of men of outstand-
ing capacity for scientific investiga-
tion and for stimulating and di-
recting the work of others along
fruitful lines. Leaders of this type
are rare, but are essential for the
success of research organisation.
With inefficient leadership, it is as
easy to waste money in research as
in other branches of human activ-
ity ”

Speaking of artificial radioactivity:

“As Fermi and his colleagues have
shown, neutrons and particularly
slow neutrons are extraordinarily ef-
fective in the formation of such
radioactive bodies. On account of
the absence of charge, the neutron
enters freely into the nuclear struc-
ture of even the heaviest element
and in many cases causes its trans-
mutation. For example, a number
of these radio-elements are produced
when the heaviest two elements,
uranium and thorium, are bom-
barded by slow neutrons. In the
case of uranium, as Hahn and Meit-
ner have shown, the radioactive bod-
ies so formed break up in a suc-
cession of stages like the natural
radioactive bodies, and give rise to
a number of transuranic elements
of higher atomic number than ura-
nium (92) . These radioactive ele-
ments have the chemical properties
to be expected from the higher
homologues of rhenium, osmium
and iridium of atomic numbers 93,
94 and 95.”

Rutherford’s death

Rutherford was not destined to go to
India. He had suffered for years from
an umbilical hernia, to relieve which
he wore a truss. On 14 Oct. 1937 he
became unwell, and was sick enough
in the night to be removed from his

home to a hospital next afternoon.
An operation for Richter’s hernia was
performed at once, and the outlook
appeared good. However, normal bow-
el movement was never reestablished,
and despite the efforts of his physi-
cians, he died of intestinal paralysis
and intoxication on 19 Oct. His great
wish at the onset of his illness was
to be well in time to fulfil his presi-
dential task in India.

Cockcroft and I were in Italy, at
the Galvani Celebrations when news
of Rutherford’s death reached us. We
were very upset and sad. At the
morning meeting on 20 Oct., before
we left to return to England, Bohr,
Rutherford’s older student and col-
league, who loved Rutherford as we
did, spoke movingly of the great man.
Afterwards, on 20 Dec., he wrote to
Lawrence thanking him for the many
kindnesses shown him, Mrs Bohr, and
their son, on his recent visit to the
Radiation Laboratory, and for his
great help in the construction of the
cyclotron in Copenhagen. His letter
ended:

“When in spite of all this I
have not written long before, it has,
however, not least been due to the
very sudden death of Rutherford
which has caused, as you under-
stand, so great upset among his
friends. Only a few weeks before
I attended his unforgetful digni-
fied funeral in Westminster Ab-
bey, I had visited him in Cam-
bridge where he was as cheerful
and enthusiastic over his work as
ever. In some way it was the most
beautiful end of his marvellous life,
but at the same time it makes the
feeling of loss ever so acute. Still,
I know that the thought of Ruther-
ford will be to you as to myself
a lasting source of encouragement
and inspiration and will be a close
bond between all of us who ad-
mired and loved him.”

To this Lawrence replied:

“Lord Rutherford’s sudden pass-
ing . . . was a great shock and
your remarks in your letter, which
I appreciated so much, are very
true. It is sad that Lord Ruther-
ford could not have lived longer,
but on the other hand we may re-
joice in the memory of his great
life. . . .

BIOGRAPHY

193

“These tragic events remind one
that life is short and uncertain and
that time is not to be wasted. I
often think that, (perhaps more so
now because of my mother’s serious
illness) that we know really so little
about the biological processes, and
we physicists should not pass by
any opportunities to be of help in
biological research, although per-
haps our first inclination would be
to devote ourselves to fundamen-
tal physical problems.”

What happened to the neutron

Rutherford had predicted the exist-
ence of the neutron in his Bakerian
Lecture to the Royal Society in June
1920. During the following years,
sometimes with the aid of research
students, he and Chadwick searched
diligently for the particle which both
were convinced was essential in the
structure of the nucleus. Many experi-
ments were made, and James Chad-
wick has given a charming personal
account of these.2 The elusive neu-
tral particle was discovered by Chad-
wick in 1932, and its effectiveness as
an agent producing nuclear transfor-
mations was established soon after-
wards by Fermi and others. Ruther-
ford was intrigued by the properties
of the neutron, and in his last lec-
ture, read posthumously by James
Jeans at the joint congress in India,
the passage that I have quoted shows
how interested he was in the produc-
tion by neutrons, in collision with
uranium, of the transuranic elements
of higher atomic number than any
existing naturally on earth. He did
not live to experience the excitement
created by the discovery by Hahn
and Strassmann in 1938, of the fis-
sion process, or the beautiful work
of Otto Frisch and Lise Meitner,
which established clearly that the ura-
nium nucleus could indeed split into
two parts when it absorbed a neu-
tron. On 9 Feb. 1939 Lawrence wrote
to Cockcroft: “We are having right
now a considerable flurry of excite-
ment following Hahn’s announce-
ment of the splitting of uranium.”

He went on to say that within a
day of reading about it in the news-
papers, they had observed the heavy
ionizing fragments produced in the
fission of uranium, and had identified

several radioactive species among
them by chemical methods.

“We are trying to find out wheth-
er neutrons are generally given off
in the splitting of uranium, and if
so, prospects for useful nuclear en-
ergy become very real.”

Lawrence was one of the few in the
United States who rapidly appreciated
the profound significance of the dis-
covery of the fission process. In Eng-
land the possibility that it had mili-
tary significance was more quickly re-
alized in particular by Frisch and
Rudolf Peierls, and by Chadwick, who
showed independently that a fast-neu-
tron fission chain process in the ura-
nium isotope of mass 235, leading to
a super-explosion, was possible. In
1941 when I visited Lawrence again,
the magnet for his giant cyclotron
was being erected on the new site
on a hillside above the campus of the
university. We discussed the general
problem, and in particular the meth-
ods that we had been considering
in Britain for the separation of the
isotopes of uranium. He was deeply
impressed by the serious view of scien-
tists in England that nuclear weapons
were not only almost certainly possi-
ble, but that Germany might be work-
ing on the problem. Soon afterwards,
he began his experiments upon the
separation of the uranium isotope by
means of the calutron, a technique
which we began to develop independ-
ently in my laboratory in Birming-
ham, using the magnet of the 60-in
cyclotron, which was being built with
the aid of information generously sup-
plied by Lawrence during and after
my visit to Berkeley in 1938. In 1943
this minor effort by us was aban-
doned in favor of cooperation with
Lawrence, and under the arrange-
ments for a joint attack on the prob-
lem of nuclear energy, made between
the governments of our countries, we
moved to Berkeley.

This is not the place to discuss
subsequent events, in which Ruther-
ford and his Cavendish Laboratory
played no part. If he had lived, he
would have rejoiced in the subsequent
triumphs of Lawrence and his col-
leagues in the Radiation Laboratory.
But he would have regretted that
his nuclear atom had become of such
practical importance that the main

motives for the financial support of
such work, in all countries, became
other than the advance of knowledge
of nature.

It was a great privilege to be the
pupil and colleague of Rutherford,
and to have known, and worked with
that other Ernest who so ably took
over the torch of nuclear physics
from him, and carried it to further
heights of achievement. Rutherford,
the greater scientist, laid the founda-
tions of modern physics. Lawrence,
with his greater flair for technology
and organization, showed how to
build, on those foundations, the mas-
sive edifice of physics today. All who
knew and worked with these great
men shared deep respect for their
genius. But they inspired more than
that. The warmth of their natures,
their generosity, and their simple, un-
assuming personalities, generated an
abiding love that made our lives fuller
and happier.

Acknowledgements

The author is grateful for the ready
access given him to correspondence
and papers in the Cambridge Univer-
sity Library and in the Lawrence
Radiation Laboratory. He acknowl-
edges the help given personally by
Sir James Chadwick, Sir John Cock-
croft, Mrs Molly Lawrence, John Law-
rence, Robert Brode, Leonard Loeb,
Raymond Birge, Edwin McMillan,
Robert Thornton, Harold Fidler, Mrs
Eleanor Davisson, Daniel Wilkes, and
many others. Luis Alvarez suggested
that the article be submitted for pub-
lication to PHYSICS TODAY.

The sketch of Rutherford by R.
Schwabe is from a copy presented
to the author by Lord Rutherford.

The portion of Birge’s history of the
Berkeley physics department covering
the period 1868 to 1932 will be avail-
able in mimeograph form (in limited
number) within the next few months.

( This is the second of two articles
on Ernest Rutherford and Ernest Law-
rence. The first appeared in the last
issue.)

□

Reference

2. J. Chadwick, Ithaca 26 VIII, 2 IX

(1962).

194

HISTORY OF PHYSICS

VAN VLECK AND MAGNETISM

Through his work on crystal field theory,

paramagnetism, resonance spectroscopy and quantum theory, one man
turned magnetism into a field too large for any one man.

PHILIP W. ANDERSON

PHYSICS TODAY / 'OCTOBER 1968

A few years ago there would have
been little need to distinguish between
the two halves of my title: John H.
Van Vleck and magnetism, as a field
of theoretical physics, were practi-
cally synonymous. Now the field has
expanded so much that no one man
can overwhelm all of its branches in
the way Van did when my generation
was being introduced to it. While I
can safely assume that all physicists
know some parts of Van’s career in
magnetism, I suspect few appreciate
the whole of it.

John Hasbrouck Van Vleck is the
son of the eminent mathematician Ed-
ward Burr Van Vleck. The only story
about our Van that is not true is that
the mathematics building at the Uni-
versity of Wisconsin is named after
him: It is named for his father. Van’s
grandfather, John Monroe Van Vleck,
was also an eminent mathematician:
The observatory at Wesleyan Univer-
sity bears his name.

Our Van Vleck received his AB at
Wisconsin in 1920 and his PhD at
Harvard only two years later at the
age of 23. He went to Minnesota in
1923, becoming a full professor in
1927. That same year he married
Abigail Pearson. A year later he
moved to his father’s university, Wis-
consin, as professor of theoretical
physics; then in 1934 he returned
to Harvard where he became a full
professor the following year.

At Harvard during World War II he
headed the theoretical group at the
Radio Research Laboratory. After the
war he became chairman of the phys-
ics department, serving until 1949.
Then he became the first dean of en-
gineering sciences and applied physics,
a position he held until 1957. In
1951 he also became Hollis Professor
of Mathematics and Natural Phil-
osophy. He plans to retire next
June.

Visiting professor

In the midst of this busy schedule, he
found time to be a visiting lecturer
on eight separate occasions, including
the Eastman Chair at Oxford (one of
the most universally envied positions
in England, since it comes with a
centrally heated house) and the Lo-
rentz professorship at Leiden. He
also has been a councillor and presi-
dent of the American Physical Society
and a vice-president of the American
Academy of Sciences, the American
Association for the Advancement of
Science and the International Union
of Pure and Applied Physics.

I shall not recite the full list of his
remaining honors, merely noting that
they are uniquely multinational: He
is a foreign member of no less than
five national academies. The Uni-
versities of Grenoble, Paris, Oxford
and Nancy are among those that have
awarded him honorary degrees; so is

Harvard, where he earned his real
one. He was the first recipient of
Case Institute’s Michelson Award and
the APS Langmuir Prize and last year
received the National Medal of Sci-
ence.

The reader may ask: “What has he
done for us lately?” A great deal, it
happens. For the past several years
he has been working on the clatlirate
compounds in which the gas molecule
is caught in a cavity or “cage” rather
than chemically bonded, so that it can
exhibit its free magnetic or other ro-
tational behavior while conveniently
trapped at the disposal of the experi-

Philip W. Anderson divides his time be-
tween a chair of theoretical physics at
Cambridge and Bell Telephone Labora-
tories. A Harvard graduate and a mem-
ber of the National Academy of Sci-
ences, he works in solid-state physics
and magnetism. This article is adapted
from a talk he gave at a session honor-
ing John H. Van Vleck during a Boston
conference on magnetism last year.

BIOGRAPHY

195

menter. He also has been working
on magnetism in the rare earths,
among other things.

Enormous influence
My emphasis, however, is on the past:
the enormous influence Van has had
on the study of magnetism, viewed as
an enterprise in the quantitative un-
derstanding of the real properties of
magnetic materials in microscopic
terms.

Van’s first work was on optical
spectra and dispersion relations in
the old quantum theory, and his
first book1 is the most complete and
elegant exposition of the old quan-
tum theory ever produced. Unfor-
tunately it was published in 1926,
just as the new quantum theory ap-
peared. This monumental piece of
bad luck did not faze him; Van was
already learning and using the new
quantum theory as it came out, and
his courses at Minnesota in that pe-
riod are remembered by his students—

including among other notables Walk-
er Bleakney and Walter Brattain— as
the most scientifically exciting courses
of their lives.

Apparently Van chose almost im-
mediately to study electric and mag-
netic susceptibilities, an area in which
the old quantum theory gave tantaliz-
ingly good results in many cases, and
to see whether the new theory was
definitely in better agreement. This
point of view, though now unfamiliar
to us, nonetheless gives his book2 a
sense of direction and cohesion that is
very welcome. He did conclude that
the new quantum theory is much bet-
ter, incidentally. His ability to carry
along an idea in each of three lan-
guages, classical and old and new
quantum theory, is one of his great-
est and most baffling strengths.

Bare bones fleshed out
It is a pleasant and fascinating task
to go back and reread that book. One
sees how even those basic ideas

originated by others are illuminated
and their bare bones fleshed out by
Van’s special point of view. One of
these is the “Heisenberg exchange
Hamiltonian,” so-called. It is true
that Werner Heisenberg first pointed
out the connection of statistics, elec-
tron exchange and ferromagnetism,
and that P. A. M. Dirac introduced
formally the connection between ex-
change and a dot product of spin op-
erators, but really it is Van Vleck who
is responsible for the Hamiltonian of
the form J 2(SfS j) that we now use
to describe magnetic insulators and
who expanded this method into the
Dirac-Van Vleck vector model, a
method capable of treating the com-
plicated coupling of the various angu-
lar-momentum vectors within atoms
and molecules as well. Again, Felix
Bloch’s spin waves take on a much
clearer form when discussed by Van.

Crystal field theory as introduced
by Hans A. Bethe was mainly an ab-
struse exercise in group theory; as
done by Van Vleck it took on the form
we still use— an effective field acting
again on those angular-momentum
vectors, in this case the orbital angu-
lar momentum of d electrons. In that
form it becomes delightfully clear
why, in some cases, the orbital angu-
lar momentum cannot respond at all
and the susceptibility is given by “spin
only”— the ubiquitous idea of “quench-
ing” orbital angular momentum.

Two things strike one in looking
back at the book from today’s point of
view. Again and again the great de-
velopments of the next decade or so,
in which Van himself often partici-
pated, were very specifically hinted
at: Antiferromagnetism and the co-
valent explanation of crystal fields are
two examples.

Van says he overlooked the possi-
bility of an ordered state when the
sign of the exchange-integral J is neg-
ative and so did not anticipate Louis
Neel and Lev D. Landau by years
in the theory of antiferromagnetism.
As it is, the proper formal theory of
this effect had to wait until he wrote
it down in 1940, six or seven years
after their rather obscure remarks.

Major contribution

The theory of crystal fields as originat-
ing from more-or-less weak covalent
bonds of the magnetic ion to its li-
gands, now accepted as one of Van’s
most important contributions to mag-
netism (after some rather regrettable
reversals), was foreshadowed in the

JOHN H. VAN VLECK, Hollis Professor of Mathematics and Natural Philosophy at
Harvard, in a photo taken last year on his 68th birthday. He will retire next June.

THE ONLY AMERICAN at the Sixth Solvay Conference at
Brussels in 1930 was Van Vleck. Here he is third from the
right in the back row. Seated in front are, left to right,
Theophile de Donder, Pieter Zeeman, Pierre Weiss, Arnold Som-
merfeld, Marie Curie, Paul Langevin, Albert Einstein, Owen
Richardson, Bias Cabrera, Niels Bohr and Wander de Haas.

In back are E. Herzen, E. Henriot, Jules Verschaffelt, C. Man-
neback, Aime Cotton, Jacques Errera, Otto Stern, Auguste
Piccard, Walther Gerlach, Charles Darwin, P.A.M. Dirac, Hans
Bauer, Peter Kapitza, Leon Brillouin, Hendrik Kramers, Peter
Debye, Wolfgang Pauli, Jakov Dorfman, Van Vleck, Enrico
Fermi and Werner Heisenberg.

196

HISTORY OF PHYSICS

book and very soon formally written
down by Van Vleck, though it had to
wait 15 years to be picked up again.

Of course, I have not mentioned
many useful and important things that
arc in the book. Van Vleck paramag-
netism is one. Another is that the
book is not “dated;” it does not at-
tempt or accept a wrong explanation
for anything, but leaves subjects open
for further ideas. A contribution de-
serving special mention is the only
really clear exposition in existence of
the meaning of Maxwell’s equations in
a medium, in terms of the actual
atoms and molecules and the real mi-
croscopic electromagnetic fields.

A second look back at Van’s career
also came from my bookshelf: a Japa-
nese reprint collection on the origins
of the field of microwave and reson-
ance spectroscopy. Virtually all of the
basic papers that were not written by
Van acknowledge his advice and con-
tribution of ideas, and of course these
we are using still. Van Vleck in his
contacts with the Dutch low-tempera-
ture group was clearly the most im-
portant figure in understanding the
nature of the relaxation of magnetic
vectors, spin-spin and spin-lattice.
He was the central figure in carrying
these concepts into radiofrequency
spectroscopy after the war.

His great papers applying Ivar
Waller’s moment method to spin-spin
relaxation and pointing out the vital
phenomenon of exchange narrowing
were of great importance; so was his
recognition of the importance to mag-
netism of the abstruse ideas of Kram-
ers (time-reversal) degeneracy— that
an odd number of electrons always
has a free spin— and of the Jahn-Teller
effect of distortion of the system in
the presence of orbital degeneracy.

Information, stimulation

Most impressive during and after the
war was his role as an information
post and stimulant for this immensely
important new field. To chat with
him at a meeting in those days was
to be interrupted by an endless parade
of experimentalists asking for an idea
or two on their latest results— and get-
ting them.

Th ree separate efforts stand out in a
very long career. All of them are
relevant to today’s events, and two of
them are cases in which Van played
a role he particularly likes: that of
mediator between two valid points of
view, emphasizing that common re-
sults of the two approaches indicated
that in the end they would turn out
to be compatible.

The first of these mediation efforts

occurred in the early days of what is
now called “quantum chemistry.”
Seemingly, two ideas that earned No-
bel Prizes many years apart— the
Slater-Pauling valence-bond idea, now
often called Heitler-London, and the
Hund-Mulliken molecular-orbital con-
cepts—conflicted in their explanations
of the chemical bond. Van Vleck
played a considerable role not only in
emphasizing that this incompatibility
need not be absolute, but in demon-
strating that both schemes could be
used to explain certain results. One
of the most important of these is that
carbon exhibits tetrahedral bonding:
The only valid discussion of this vital
fact to this day, in my opinion, was in
his papers in the Journal of Chemical
Physics during this period.

Results not incompatible

A second instance involved the series
of papers and reviews he produced,
from the late 1930’s onward, empha-
sizing that the local spin and itinerant
models of ferromagnetism need not be
incompatible, and gave many similar
results. In fact, with our present un-
derstanding of spin waves as collective
excitations of the itinerant model and
of the nature of spin phenomena in
metals and insulators, this must be
described as the only possible point of

197

ies about him are true: He does own
a great collection of Japanese wood-
block prints, inherited from his father,
many acquired from Frank Lloyd
Wright. He was for years the world’s
greatest expert on obscure railway
timetables.

It is true that he once rode to Bell
Laboratories from New York in the
cab of the Phoebe Snow. I am par-
ticularly grateful for one of his rides:
When I graduated from Harvard, Van
took the Phoebe Snow to Bell Labs
and talked them into taking a chance
on me. It is also true that he has
had two papers published in the An-
nals of the National University of Tu-
cuman in Mexico.

Students challenged

Many of his students remember his
habit of asking the class for a response
—typical was the day when he came
into class and started his lecture with:
“A clever trick is what?” We also re-
member his group-theory course in
which we learned most of the subject
through a diabolical series of prob-
lems. He once wrote a problem on
the blackboard as DOOCS and it took
us a while to realize that he meant:
“Do the molecule OCS.”

The problems usually were short
but had terribly long hints. We
learned early that you should read the
hint only after doing the problem,
when it very likely would give you an
entirely new insight in what you had
done. But we ordinary mortals sel-
dom were able to do the problems
that way.

No one I have ever heard of came
out of a Van Vleck course without
having learned, usually having learned
a great deal. The list of his students
is so large and so eminent that it is
hardly fair to pick out any suitable
subset of names: Let me drop the
names of, say, Robert Serber, John
Bardeen and Harvey Brooks at ran-
dom.

John Van Vleck laid the founda-
tions in a field that has kept a genera-
tion of physicists busy. Many in the
field owe the beginnings of their ca-
reers to him. This article is an at-
tempt to show our appreciation.

References

1. Van Vleck, Quantum Principles and
Line Spectra, National Research Coun-
cil, Washington (1926).

2. Van Vleck, Theory of Electric and

Magnetic Susceptibilities, Clarendon
Press, Oxford (1932). □

BIOGRAPHY

view. Either perfect itineracy or per-
fect localization is very rare, and no
magnetic phenomenon should be
looked at exclusively from one point
of view or the other. As Conyers
Herring put it in a famous review, it
is all a matter of how you mix your
cocktails, but neither pure gin nor
pure vermouth is very satisfactory.

A final contribution that crops up
these days in such diverse areas as
intergalactic hydroxyl-maser effects
and satellite communications is Van
Vleck’s yeoman work over the years on

molecular spectra in all their fascinat-
ing complication. It is his work on
lambda doubling on which our knowl-
edge of the hydroxyl spectrum is
based, and it was his calculations on
CL that explained the opacity of the
atmosphere in certain millimeter-
wavelength regions of the spectrum
that otherwise woidd be ideal for sat-
ellite communications.

The teacher and the person

Then there is Van the teacher and
Van the person. Almost all the stor-

AT MINNESOTA in 1925, Van Vleck (second from left in second row) is flanked on
the left by Joseph Valasek and on the right by John Tate. Others in the picture in-
clude J. William Buchta (eighth from left in back row), Elmer Hutchinson (ninth
from left, back row) and Walker Bleakney (tenth from left, back row).

AT WISCONSIN about 1929, Werner Heisenberg (first row, center) posed with the
physics faculty. Van Vleck sits next to him at left. Also in picture are Leland Howarth
(seventh from left, back row) and Albert Whitford (second from right, back row).

198

HISTORY OF PHYSICS

Alfred Lee Loomis —
last great amateur of science

This multimillionaire banker, who for years led a double life, spending days
on Wall Street and evenings and weekends in his private physics laboratory,
became one of the most influential physicists of the century.

Luis W. Alvarez physics today / January 1983

The beginning of this century marked a
profound change in the manner in
which science was pursued. Before
that time, most scientists were inde-
pendently wealthy gentlemen who
could afford to devote their lives to the
search for scientific truth — Lord Cav-
endish, Charles Darwin, Count Rum-
ford, and Lord Rayleigh come to mind.
But after the turn of the century,
university scientists found it possible to
earn a living teaching students, while
doing research “on the side.” So the
true amateur has almost disappeared —
Alfred Loomis may well be remem-
bered as the last of the great amateurs
of science. He had distinguished car-
eers as a lawyer, as an Army officer and
as an investment banker before he
turned his full energies to the pursuit
of scientific knowledge, first in the field
of physics and later as a biologist. By
any measure that can be employed, he
was one of the most influential physical
scientists of this century:

► He was elected to the National
Academy when he was 53 years old

► He received many honorary degrees
from prestigious universities

► He played a crucial role as director
of all NDRC-OSRD radar research in
World War II.

Family background

Loomis was born in New York City
on 4 November 1887. His father was
Dr. Henry Patterson Loomis, a well-
known physician and professor of clini-
cal medicine at New York and Cornell
medical colleges. His grandfather, for
whom he was named, was a great
nineteenth-century tuberculosis spe-
cialist. His maternal uncle was also a
physician, as well as the father of
Alfred Loomis’ favorite cousin, Henry

Alfred Lee Loomis in his early seventies at
the Rand Corporation circa 1963.

■■■■■

BIOGRAPHY

199

L. Stimson, who was Secretary of State
under Herbert Hoover, and Secretary
of War throughout World War II.

From Alfred Loomis’ educational
background, one would correctly judge
that he came from a prosperous, but
not exceedingly wealthy family. He
attended St. Matthew’s Military Aca-
demy in Tarrytown, New York, from
the age of nine until he entered An-
dover at thirteen. His early interests
were chess and magic; in both fields, he
attained near-professional status. He
was a child prodigy in chess, and could
play two simultaneous blindfold games.
He was an expert card and coin manip-
ulator, and he also possessed a collec-
tion of magic apparatus of the kind
used by stage magicians. On one of the
family summer trips to Europe, young
Alfred spent most of his money on a
large box filled to the brim with folded
paper flowers, each of which would
spring into shape when released from a
confined hiding place. His unhappiest
moment came when a customs inspec-
tor, noting the protective manner in
which the box was being held, insisted
that it be opened — over the strong
protests of its owner. It took a whole
afternoon to retrieve all the flowers.

The story of the paper flowers is the
only story of Loomis’s childhood I can
remember hearing from him. In the
thirty-five years during which I knew
him rather intimately, I never heard
him mention the game of chess, and his
homes contained not a single visible
chessboard or set. (When I checked
this point recently with Mrs. Loomis,
she wrote, “Alfred kept a small chess
set in a drawer by his chair and would
use it, on and off, to relax from other
intellectual pursuits. He preferred
solving chess problems or inventing
new ones to playing games with other
people.”)

He loved all intellectual challenges
and most particularly, mathematical
puzzles. He made a serious attempt to
learn the Japanese game of Go, so that
he could share more fully in the life of
his son Farney, who was one of the best
Go players in the US. But his chess
background wasn’t transferable to the
quite different intricacies of Go, and he
had to be content to collaborate with
his son in their researches on the
physiology of hydra. As he grew older
his manual dexterity lessened, but he
still enjoyed showing his sleight-of-
hand tricks to the children of his
friends and to his grandchildren — but
never to adults.

It was characteristic of Loomis that
he lived in the present, and not in the
past the way so many members of his
generation do. He apparently felt it

Luis W. Alvarez is professor emeritus in the
department of physics at the University of
California, Berkeley, California.

would sound as though he were brag-
ging if he alluded to the great power he
once wielded in the financial world
when in the company of a university
professor. In 1940, I casually asked
him what he thought of Wendell Will-
kie, the Republican presidential candi-
date, and he said, “I guess I’ll have to
say I approve of him because I appoint-
ed him head of Commonwealth and
Southern.” Loomis was the major
stockholder of that utility, so there was
certainly an element of truth in his flip
and very uncharacteristic remark. He
was immediately and obviously embar-
rassed by what he had said, and it
would be another twenty years before
he made another reference to his finan-
cial career in my presence.

Loomis entered Yale in 1905, where
he excelled in mathematics, but he was
not interested enough in the formali-
ties of science to enter Sheffield Scienti-
fic School. He took the standard gent-
lemen’s courses in liberal arts, and
without giving much thought to his
career, felt he would probably engage
in some kind of scientific work after he
graduated. But one afternoon, a close
friend came to him for advice on
choosing a career. Loomis strongly
urged him to go to law school, pointing
out that a broad knowledge of the law
was a wonderful springboard to a

variety of careers: In addition to formal
legal work, a lawyer was well prepared
for careers in business, politics, or
government administration. Loomis
was so impressed by the arguments he
marshaled for his friend that he en-
rolled in Harvard Law School. He
never regretted that decision, because
it gave him a breadth of vision that he
applied to many fields.

In his senior year at Yale, he was
secretary of his class, but he had the
time and the financial resources to
pursue his life-long hobby of “gadge-
teering.” His extracurricular activities
involved technical matters such as the
building of gliders, model airplanes,
and radio-controlled automobiles. He
was fascinated by artillery weapons,
and we shall learn that the great store
of information he accumulated in that
field played a crucial role in changing
the major focus in his life from business
to the world of science. A glider he
built and tested from the dunes near
his summer home at East Hampton
stayed in the air several minutes. It
was obvious to his friends that he was
distinguished by a wide-ranging mind

R. W. Wood became a close friend of
Loomis in the 1920s and served in effect as
his private tutor in physics. (Photo courtesy
of the AIP Niels Bohr Library.)

200

HISTORY OF PHYSICS

and the ability to learn all about a
completely new field in a remarkably
short time through independent read-
ing. That facet of his personality and
intellect was the most immutable
throughout his life — a life that would
be characterized by periodic and major
changes of interest.

Loomis’s decision to become a lawyer
was certainly influenced by his cousin,
Henry Stimson, in whose firm of Win-
throp and Stimson he was assured a
clerkship. But after his distinguished
performance at Harvard Law School —
where he was in the “top ten,” helped
edit the Harvard Law Review , and
graduated cum laude in 1912 — he
would have been welcomed in any New
York law firm. As one would guess
from his later interests, he specialized
in corporate law and finances.

Early career

Loomis’s career as a young corpora-
tion lawyer was interrupted by World
War I. When he joined the Army, his
fellow officers were surprised to learn
that he knew much more about modern
field artillery than anyone they had
ever met. He had made good use of the
special communication channels avail-
able to Wall Street lawyers, and had
accumulated a vast store of up-to-the-
minute data on the latest ordnance
equipment available to the warring
European powers. His expertise in
such matters led to his assignment to
the Aberdeen Proving Grounds, where
he was soon put in charge of experi-
mental research on exterior ballistics,
with the rank of major. At Aberdeen,
he was thrown into daily contact with
some of the best physicists and astron-
omers of this country, and he and they
benefited from each other’s talents.

In those days, before photoelectric
cells and radar sets came to the aid of
exterior ballisticians, there was no
convenient way to measure the velocity
of shells fired from large guns. Loomis
invented the Aberdeen Chronograph,
which satisfied that need for many
years after its invention. It is hard for
someone like me, who came into a scene
long after an ingenious device had been
invented, and later supplanted, to ap-
preciate what made that device so
special. But the fact that Loomis sin-
gled out the Aberdeen Chronograph for
mention in his entries in Who's Who
and American Men and Women of
Science, and mentioned it on a number
of occasions in conversations with me,
makes me believe that it must have
been a remarkably successful and im-
portant invention. Loomis set such
high standards for his own perfor-
mance that no other interpretation of
the value of the Aberdeen Chronograph
would be consistent with his pride in it.

One of the friends Loomis made at
Aberdeen was Robert W. Wood, who

was considered by many to be the most
brilliant American experimental
physicist then alive. They had known
each other casually from the circum-
stance that each of their families had
summer homes at East Hampton, on
Long Island. But at Aberdeen, they
initiated a symbiotic relationship that
lasted many years. Wood became, in
effect, Loomis’s private tutor, and he
responded by becoming Wood’s scienti-
fic patron. The following paragraphs
from Wood’s biography, tell of this
relationship better than anyone of the
present era could:1
It was a consequence of Wood’s
scientific zest and social strenuous-
ness that fate brought him, about
this time, the facilities of a great
private laboratory backed by a
great private fortune. He had met
Alfred Loomis during the war at
the Aberdeen Proving Grounds,
and later they became neighbors
on Long Island. Loomis was a
multimillionaire New York bank-
er whose lifelong hobby had been
physics and chemistry. Loomis
was an amateur in the original
French sense of the word, for
which there is no English equiva-
lent. During the war, he had
invented the “Loomis Chrono-
graph” for measuring the velocity
of shells. Their relationship, re-
sulting in the equipment of a
princely private laboratory at Tux-
edo Park, was a grand thing for
them both.

A happy collaboration began,
which came to its full flower in
1924. Here is Wood’s story of what
happened.

“Loomis was visiting his aunts at
East Hampton and called on me
one afternoon, while I was at work
with something or other in my
barn laboratory. We had a long
talk and swapped stories of what
we had seen or heard of science in
warfare. Then we got onto the
subject of postwar research, and
after that he was in the habit of
dropping in for a talk almost every
afternoon, evidently finding the
atmosphere of the old barn more
interesting if less refreshing than
that of the beach and the country
club.

"One day he suggested that if I
contemplated any research we
might do together which required
more money than the budget of the
physics department could supply,
he would like to underwrite it. I
told him about Langevin’s experi-
ments with supersonics [what is
now called “ultrasonics”] during
the war and the killing of fish at
the Toulon Arsenal. It offered a
wide field for research in physics,
chemistry, and biology, as Lange-

vin had studied only the high-
frequency waves as a means of
submarine detection. Loomis was
enthusiastic, and we made a trip to
the research laboratory of General
Electric to discuss it with Whitney
and Hull.

“The resulting apparatus was
built at Schenectady and installed
at first in a large room in Loomis’
garage at Tuxedo Park, New York,
where we worked together, killing
fish and mice, and trying to find
out whether the waves destroyed
tissue or acted on the nerves or
what.

“As the scope of the work ex-
panded we were pressed for room
in the garage and Mr. Loomis
purchased the Spencer Trask
house, a huge stone mansion with a
tower, like an English country
house, perched on the summit of
one of the foothills of the Ramapo
Mountains in Tuxedo Park. This
he transformed into a private la-
boratory deluxe, with rooms for
guests or collaborators, a complete
machine shop with mechanic and a
dozen or more research rooms
large and small. I moved my forty-
foot spectrograph from East
Hampton and installed it in the
basement of the laboratory so that
I could continue my spectroscopic
work in a better environment . . .”

Loomis, who was anxious to
meet some of the celebrated Euro-
pean physicists and visit their labo-
ratories, asked Wood to go abroad
with him. They made two trips
together, one in the summer of
1926, the other in 1928.

Business career

After World War I, Loomis formed a
lifelong business partnership with Lan-
don K. Thorne, his sister Julia’s hus-
band: In the thirty-five years I was so
personally close to Loomis, I met
Thorne on only two occasions. Loomis
kept his business friends and his scien-
tific friends quite separate. For a long
time, he apparently reasoned that
while his broad range of interests made
both groups exceedingly interesting to
him, the two disparate groups might
not feel about each other as he did
about them. As he grew older, Loo-
mis’s personal ties to the scientific
world became the dominant ones, and I
find that his last entry in Who’s Who in
America lists his occupation simply as
“Physicist.”

Loomis was proud of the fact that he
and Thorne were in many kinds of
business deals, and in every one of
them, they were equal partners. First
of all, they had equal shares in the very
profitable Bonbright and Co., the in-
vestment banking firm of which Lan-
don was the president, and Loomis the

BIOGRAPHY

201

vice-president. This firm was instru-
mental in putting together and financ-
ing many of the largest public utilities
in the country.

The two partners also built a very
innovative racing sloop of the J-class,
which they hoped would win the right
to race against Sir Thomas Lipton in
one of his periodic attempts to capture
the America’s Cup from the New York
Yacht Club. To cut down on wind
resistance, the partners arranged to
have most of the crew below decks at all
times, working levers in the fashion of
galley slaves, rather than hauling on
wet lines on the deck. With the help of
the MIT naval architecture depart-
ment, they did a thorough study of hull
shapes, and there were several changes
in the location of the mast — made of
strongest and lightest aluminum al-
loy— during the test program. But in
spite of all these efforts, Whirlwind
wasn’t a success. Perhaps the best
indicator of Loomis’s financial state at
that time is that J-boats were then
almost always built by “syndicates” of
wealthy men such as the Vanderbilts.
But to have complete control of their J-
boat, Loomis and Landon paid for the
whole project, 50-50 as always. After
World War II, J-boats became too
expensive even for syndicates of rich
men, so the America’s Cup races are
now sailed in the smaller “12-meter”
boats.

Another of Loomis and Thorne’s
partnership was the ownership of Hil-
ton Head, an island off the coast of
South Carolina. Hilton Head is now a
famous resort area, with luxurious
hotels and golf courses. But when
Loomis and Landon owned it, it was
completely rustic. They used it only for
riding and hunting, and invited their
friends to share the beauties of the
place with them. They also owned a
large oceangoing steam yacht, which
they donated to the Navy at the start of
World War II. I can count on the
fingers of one hand the number of times
I’ve seen Loomis’s name in the public
press — he believed that the ideal life
was one of “prosperous anonymity.”
The first time I saw his name in print
was when Time identified him as a
“dollar-a-yacht man,” one of several
who had given their yachts to the Navy
in return for a dollar. Recently, I’ve
found in the library two old articles
about Loomis. The first was a popular
article on the unusual J-boat and its
owners. The second was an article in
the very first issue of Fortune concern-
ing Wall Street firms, and telling of the
great success of Bonbright and Co., its
well-known president, Landon Thorne,
and its shadowy and brilliant vice-
president, Alfred Loomis, who kept in
the background and planned their fi-
nancial coups. According to the article,
“Bonbright . . . rose in the twenties

from near bankruptcy to a status as the
leading US investment-banking house
specializing in public-utility securi-
ties.”

Tuxedo Park laboratory

When the Fortune article appeared,
Loomis was leading a double life; his
days were spent on Wall Street, but his
evenings and weekends were devoted to
his hilltop laboratory in the huge stone
castle in Tuxedo Park. The laboratory
was abandoned in November 1940, so
those who worked in it could join the
newly established MIT Radiation La-
boratory that Loomis was instrumental
in founding, and which reported direct-
ly to him, in his wartime role as head of
the NDRC’s Radar Division. I arrived
at MIT at the same time, so I learned
much about the Tuxedo Park labora-
tory from the young scientists and
engineers who had worked there
throughout the year, and from the
former laboratory manager, P. H. Mill-
er. The following account of a labora-
tory I never visited is based on those
recollections, and on stories I heard
from older physicists who had been
Loomis’s guests during summers at
Tuxedo, and finally on the countless
reminiscences of Loomis and other
members of his family.

Because of Wood’s strong influence,
the laboratory concentrated at first on
problems that interested him. As the
quotations from his biography tell, the
first major work was in ultrasonics.
Loomis and Wood are still mentioned
in the introductory chapters of text-
books on ultrasonics and sometimes
referred to as the “fathers of ultrason-
ics.” The field has grown enormously
since they did their pioneering work,
and it now has practical applications in
industrial cleaning, emulsifying, and
most recently in medical imaging, in
place of x rays when the required
moving pictures would involve exces-
sive radiation doses. Imaging ultra-
sonic scanners are now in common use
to watch the motion of heart valves, to
observe fetuses, and at the highest
frequencies, they serve as high resolu-
tion microscopes.

A bound volume of the “Loomis
Laboratory Publications” (1927-1937)
includes reprints of sixty-six scientific
papers, of which twenty-one were on
ultrasonics; Loomis was a co-author of
the first four, and of four later ones.
The first is the classic 1927 paper by
Wood and Loomis, some of whose re-
sults are described by Wood in the
quotation above.

The laboratory was well equipped for
work in Wood’s specialty of optical
spectroscopy. Ten papers in this field
came from the laboratory, including
one by Loomis and George B. Kistia-
kowsky entitled “A Large Grating
Spectrograph,” which illustrates Loo-

mis’ talents as an innovative designer
of precision mechanical devices. None
of the spectroscopic papers bear his
name; it wasn’t in his nature to publish
in a mature field. Although Loomis
admired those who could do the in-
volved spectroscopic analyses that
came from his laboratory, he preferred
to do the pioneering work in some new
field. His admiration for the real
professionals of this era is shown by the
fact that he arranged a series of confer-
ences in honor of visiting European
physicists. Guests at the conferences
were transported to Tuxedo Park in a
private train, and entertained in lavish
style at the laboratory. The Journal of
the Franklin Institute , in the issue of
April 1928, has a sixty-five page section
entitled “Papers Read at a Conference
in Honor of Professor [James] Franck,
at the Loomis Laboratories, Tuxedo,
New York, January 6, 1928.” Included
are papers by Franck, Wood, Karl
Taylor Compton, and several others.

I have no records of the other confer-
ences, but Loomis once showed me the
guest book from the laboratory. (It had
just been returned to him by his son,
Farney, when the latter had closed his
“Loomis Laboratory” to join the Bran-
deis University faculty.) The book
showed the names of most of the well-
known American and European physi-
cists of the period. On some occasions,
a page with many famous names would
be headed by the name and the man in
whose honor the group had assembled.
Most often such an honored guest was a
visiting European physicist, for exam-
ple, Einstein, Bohr, Heisenberg, or
Franck.

Loomis’s main interest at that time
was in accurate time-keeping. The
following quotation from Wood’s biog-
raphy will serve to introduce that
subject:2

Wood’s second trip abroad with
Alfred Loomis was made in 1928.
They called first on Sir Oliver
Lodge, who presented each of them
with an autographed copy of his
latest book, Evidence of Immortal-
ity .. .

One of the things Loomis hoped
to obtain in England was an astro-
nomical “Shortt clock,” a new in-
strument for improving accuracy
in measurement of time. It had a
“free pendulum” swinging in a
vacuum in an enormous glass cyl-
inder— and was so expensive that
only five of the big, endowed obser-
vatories yet possessed one. Says
Wood:

“I took Loomis to Mr. Hoke-
Jones, who made the clocks. His
workshop was reached by climbing
a dusty staircase, and there was
little or no machinery in sight, but
one of the wonderful clocks was
standing in the corner, almost

202

HISTORY OF PHYSICS

Ernest O. Lawrence

and Loomis developed
quick friendship when
they first met in 1 939
at Berkeley. Loomis
helped obtain backing
of scientific
establishment for
Lawrence’s 184-inch
cyclotron and $2.5
million funding from the
Rockefeller
Foundation. (Courtesy
of Watson Davis,
Science Service.)

completed, which made the total
production to date six. Mr. Loomis
asked casually what the price of
the clock was, and on being told
that it was two hundred and forty
pounds (about $1200), said casual-
ly. ‘That’s very nice. I’ll take
three,’ Mr Jones leaned forward,
as if he had not heard, and said, ‘I
beg your pardon?’ ‘I am ordering
three,’ replied Mr. Loomis. ‘When
can you have them finished? I’ll
write you a check in payment for
the first clock now.’

Mr. Jones, who up to then had
the expression of one who thinks
he is conversing with a maniac,
became apologetic. ‘Oh no,’ he said,
‘I couldn’t think of having you do
that, sir. Later on, when we make
the delivery, will be quite time
enough.’ But Loomis handed him
the check nevertheless.”

Back in America, they learned
that Professor James Franck, Nobel
prize winner, was coming over in
January to give lectures at various
universities. Wood suggested to Loo-
mis that he hold a congress of
physicists in his Tuxedo Park labora-

tory in Franck’s honor. Franck
accepted and the meeting was held
in the library, a room of cathedral-
like proportions, with stained-glass
windows. Franck gave his first
lecture in America there; Wood,
Loomis, and others made subsequent
addresses. The visiting American
physicists were conducted through
the laboratory and shown the super-
sonic and other experiments. The
congress in this palace of science
proved such a success that it was
repeated the following year.

Loomis’s interest in accurate time-
keeping probably resulted from his
seagoing background, and his fascina-
tion with the art and science of naviga-
tion. He installed the three Shortt
clocks on separate brick piers that were
isolated from the laboratory structure,
and extended down to bedrock. He was
surprised to find that the clocks beat
for long times in exact synchronism,
and thought at first that they were
locked together by gravitational inter-
actions between the pendula. But he
found that the coupling was through
the bedrock, so the clocks were then

placed at the corners of an equilateral
triangle, facing inward, and the cou-
pling was broken.

The Bell Telephone Laboratories had
at the time been developing quartz
crystal oscillators with low tempera-
ture coefficients, and they came to
surpass the Shortt clocks for short-
term accuracy, but not for periods
greater than a day. Loomis had a
private line installed to carry the Bell
oscillator signals to his horological
laboratory, and he designed an inge-
nious chronograph to compare the
timekeeping abilities of the Shortt pen-
dulum clocks with the quartz oscilla-
tors. Because the first of these types
was sensitive to gravity but the second
was not, Loomis used his chronograph
to demonstrate the expected but pre-
viously undetected effect of the moon
on pendulum clocks. Loomis accumu-
lated the observational data himself,
but the data analysis required the
services of a battery of “computers” —
women who operated desk-top comput-
ing machines, and whose salaries were
paid by Loomis. The results of the
analysis were published by Ernest W.
Brown and Dirk Brouwer in a paper
immediately following Loomis’s “The
Precise Measurement of Time,” in the
Monthly Notices of the Royal Astro-
nomical Society, March 1931.

Loomis published several papers on
biology and physiology with E. Newton
Harvey and Ronald V. Christie. I
never heard him speak of the physiolo-
gical work, but he was obviously proud
of the microscope-centrifuge he devel-
oped with Harvey. This was typical
Loomis “gadget” of the kind he enjoyed
building all his life. The device made is
possible for a biologist to watch for the
first time the deformation of cells
under high “g-forces.” As Harvey and
Loomis said in the introduction to their
first paper on the subject.3
The previous procedure has been
to centrifuge the cell in a capillary
tube, remove it from the tube and
observe it under a microscope to
determine what happens. It would
obviously be far better to observe
the effect of centrifugal force while
the force was acting. . . . Our com-
munication describes a practical
means of attaining this end.

In typical Loomis fashion, his name
appears on only the first of thirteen
papers on the microscope-centrifuge
that are to be found in the collected
reprints of the laboratory.

In the mid-thirties, Loomis turned
his attention to the newly discovered
brain waves. Hans Berger had pub-
lished his observations in the German
literature, but American physiologists
were unable to duplicate his results,
and most of them apparently doubted
the existence of the very low voltage
signals that Berger described. From

BIOGRAPHY

203

his contacts with industry, Loomis had
available the best amplifiers, and he
did his work inside “a screen cage,” to
eliminate interfering electrical noise.
He had by this time retired from his
Wall Street firm, and was devoting his
full attention to his scientific work.
For this reason, his name appears on
all of the laboratory papers on brain
waves, many of which were of great
importance. His work erased any lin-
gering doubts concerning the value of
Berger’s discovery; electroencephalo-
grams are now used routinely in the
diagnosis of epilepsy and many other
diseases. In fact, one finds advertise-
ments in magazines for “bio-feedback
devices” that let the user observe his
Berger “alpha waves,” and learn to
control them, “leading to greater crea-
tivity.” (In kit form, $34.95.)

Loomis and his coworkers investigat-
ed many aspects of brain waves and did
particularly important work with
sleeping subjects that involved the
abrupt changes in the character of the
waves as the subject underwent “quan-
tum jumps” in his “depth of sleep.” It
was then possible to tell precisely when
a subject dropped from one of five
states of sleep from which he could
instantly be awakened by a small
disturbing noise, into one in which he
would fail to respond to the loudest
noises that Loomis’s high-fidelity am-
plifiers could produce. (Loomis was one
of the first “hi-fi buffs”; his homes were
always filled to overflowing with a
changing parade of the latest and most
advanced high-fidelity sound-reproduc-
ing equipment. Avery Fisher and
Loomis were personally close, and on at
least one occasion, Fisher improved his
superb product line with an idea that

Loomis had devised to make the fidelity
even higher.)

The only formal scientific talk I ever
heard Loomis give was the the weekly
physics-department colloquium in
Berkeley, in 1939. He described his
important brain-wave experiments on
sleeping, hypnotized, and blind sub-
jects.

In 1939, Loomis’s scientific interests
changed drastically. He became deeply
involved in Ernest Lawrence’s projects
and he shifted the emphasis of his own
laboratory from pure science to war-
related technology, by starting the
construction of a microwave radar sys-
tem to detect airplanes. The Sperry
Gyroscope Company had brought an
interest in the klystron patents that
were owned by the Varian brothers,
who invented the klystron, and Stan-
ford University, which had supported
the development work. Sperry built a
small klystron plant in San Carlos,
near Stanford, and their first customer
was Alfred Loomis, who appeared,
checkbook in hand, as he had years
before at the small plant making
Shortt clocks.

Work with Lawrence

I was not surprised to meet Loomis in
Berkeley, on his first visit to the
Radiation Laboratory, in 1939. Francis
Jenkins of the Berkeley physics depart-
ment had spent a summer at Tuxedo as
Loomis’s guest, and he had told me in
wide-eyed amazement about the fantas-
tic laboratory at Tuxedo Park, and
about the mysterious millionaire-
physicist who owned it. Everyone who
had submitted an article to the Phys-
ical Review in the depression years had
received a bill for page charges togeth-

er with a note saying that in the event
the author or his institution was un-
able to pay the charges, they would be
paid by an “anonymous friend” of the
American Physical Society. There was
of course no way to break the veil of
secrecy surrounding the “anonymous
friend,” but Jenkins told me in confi-
dence that he felt sure that Loomis was
the Society’s benefactor. (That was a
correct surmise.) Jenkins told me that
Loomis was a wonderful person, but he
didn’t like the other residents of Tux-
edo Park. He thought they were too
“snooty,” and looked down on the
scientists as barbarians who “didn’t
even dress for dinner.”

The relationship that quickly devel-
oped between Loomis and Ernest Law-
rence had all the earmarks of a “perfect
marriage”: They were completely com-
patible in every sense of the word, and
their backgrounds and talents comple-
mented each other almost exactly.
Lawrence was a country boy from
South Dakota and the first faculty
member of a state university to win a
Nobel prize. He had developed an
entirely new way of doing what came to
be called "big science,” and that devel-
opment stemmed from his ebullient
nature plus his scientific insight and
his charisma; he was more the natural
leader than any man I’ve met. These
characteristics attracted Loomis to
him, and Loomis in turn introduced
Lawrence to worlds he had never
known before, and found equally fasci-
nating. Anyone who was in their
company from 1940 until Lawrence
died in 1958 would have thought that
they were lifelong intimate friends
with all manner of shared experiences
going back to childhood.

Meeting of top

physicists in 1 940 to
discuss plans for 184-
inch cyclotron included
(left to right) Ernest O.
Lawrence, Arthur H.
Compton, Vannevar
Bush, James B.
Conant, Karl T.
Compton and Loomis.
(Courtesy of Lawrence
Radiation Laboratory.)

204

HISTORY OF PHYSICS

I was impressed by the way Loomis
would seek out the younger members of
the laboratory to learn everything he
could about us and what we were doing
and planning to do in our next round of
experiments. I had never before had
any serious discussions of physics with
anyone as old as Loomis, and I was
pleased that he liked to visit with me
after I had taught a freshman class and
was sitting out my required “office
hour” — waiting to talk with the stu-
dents who seldom came by. We talked
a lot about physics, and found we were
simpatico. He taught me an important
lesson that I have put to good use in my
life: The only way a man can stay
active as a scientist as he grows older is
to keep his communication channels
open to the youngest generation — the
front-line soldiers.

Although Loomis’s real mission in
coming to Berkeley was to help Law-
rence raise the funds to build the 184-
inch cyclotron, he also used the time to
learn everything he could about cyclo-
tron engineering and nuclear physics.
I remember one occasion when I men-
tioned in passing that because of the
war in Europe, the price of copper had
risen to almost twice that of aluminum,
for a given volume. Since aluminum
had only 60 percent more specific
resistivity than copper. I suggested to
Loomis that aluminum might now be
the preferred metal for the magnet
windings of the 184-inch cyclotron. It
seemed obvious to me, from elementary
scaling laws, that an aluminum coil
would be larger but would cost less. I
had completely forgotten the sugges-
tion, when a few days later, Loomis
showed me a long set of calculations
based on several altered designs of the
184-inch cyclotron that proved my snap
judgment wrong. I came to appreciate
for the first time the difference
between the world of business, where a
20 percent decrease in cost was a major
triumph, and the world of science,
where nothing seemed worth doing
unless it promised an improvement of a
factor of ten. I hadn’t done the calcula-
tions concerning the cyclotron cost
because they obviously didn’t permit a
“large” savings in cost. But Loomis
considered it worth a day or two of his
time to see if he could cut the cost of the
magnet windings by $50 000.

Lawrence once told me of spending
some time with Loomis in New York,
after the Rockefeller Foundation had
allocated $2.5 million to build the 184-
inch cyclotron. Earlier, Loomis had
been instrumental in securing the vir-
tually unanimous backing of the
“scientific establishment” for the pro-
posal, thus relieving the Rockefeller
Foundation of any necessity for acting
as a judge between factions competing
for the largest funds ever given to any
physics project. So after acting as a

senior statesman in the worlds of
science and philanthropy, Loomis was
ready to help Lawrence obtain the best
possible bargains in the purchase of
iron and copper for the giant cyclotron.
Lawrence recalled that after spending
some time with the Guggenheims, dur-
ing which a favorable price for copper
was negotiated, Loomis said, “Well,
now we have to go after the iron. I
think Ed Stettinius is the right man.”
(Stettinius was then Chairman of US
Steel, and later Secretary of State.)
Lawrence was impressed when a call
was put through and Loomis said,
“Hello Ed, this is Alfred, I have some-
one with me I think you’d like to meet.
When can we come over?” They were
soon in Stettinius’ office, and shortly
after Lawrence had given him a pitch
on the great cyclotron, he and Loomis
were in the latter’s apartment celebrat-
ing their success with a drink.

Radar development

In early 1940, Loomis was back in
Berkeley, and he told me that his next
big project was to arrange for the
funding of Enrico Fermi’s embryonic
plans to build a nuclear chain reactor.
I hadn’t given any thought to the
problems involved in designing or
building such a device, so everything
Loomis told me was most interesting.
But his involvement in reactors was cut
short in the summer of 1940 by the
dramatic appearance in Washington of
the “Tizard Mission.” The purpose of
this group of visiting British scientists
was to enlist the help of the United
States in developing and building the
new devices needed to meet the mili-
tary requirements of a war that had
become technologically oriented to a
degree quite unappreciated by our mili-
tary-industrial-scientific establish-
ment. As an example, radar had been
invented independently in the United
States by the Navy and the Army, and
in England by Robert Watson-Watt.
The US military departments treated
the subject with such excessive secrecy
that no “outsiders” learned of it. Since
the outsiders were the real profession-
als in radio engineering, they were the
ones who could have developed Ameri-
can radar into the useful military tool
that the insiders didn’t manage to
achieve. (The dismal state of US radar
was demonstrated at Pearl Harbor, a
year and a half after the Tizard Mission
had revealed all the British successes to
the US armed forces.)

The world now knows that the oper-
ational success of the long-wave British
radar was the foundation on which the
RAF triumphs of the Spitfire and
Hurricane pilots were based. A second
generation of VHF radar, in the 200-
MHz (1.5-m) band, could be fitted into
planes to turn them into night fighters
and anti-submarine patrols. Everyone

agreed that microwave radar in the
3000-MHz ( 10-cm) band would be vastly
superior to the 1.5-m equipment then
available. But there appeared to be
little chance that a powerful generator
of such pulsed microwaves could be
developed.

When John T. Randall and Henry
Boot made their breakthrough with the
cavity magnetron in Mark Oliphant’s
laboratory in Birmingham, it was sud-
denly clear that microwave radar was
there for the asking, but Britain had no
spare “bodies” who could be asked to do
the development — everyone with appli-
cable skills was working at breakneck
speed on the immediate problems of a
desperate war that could be lost any
day by the starvation of the submarine-
blockaded British people. So, in a great
and successful gamble, Winston Chur-
chill made the decision to share all of
his country’s technical secrets with the
United States, in the hope that the
potential gain would offset the loss in
compromised security. Sir Henry Ti-
zard was sent to Washington with a
committee of experts, including such
luminaries as Sir John Cockcroft, to
brief their American counterparts on
all aspects of the scientific war.

Loomis was included in the briefings
not only because of his unique position
in the scientific establishment, but
because his laboratory had built one of
the two microwave radar sets then
existing in the United States. Both
were based on the klystron tube recent-
ly invented by Russell and Sigurd
Varian at Stanford University, and
both were “continuous-wave Doppler
radars” of the type now used by police
departments to apprehend speeders.
William Hansen, who designed the first
of these microwave radar sets, attempt-
ed for the next few years to find a
wartime niche for such a device, but
without much success. Loomis immedi-
ately sensed the great superiority of the
pulsed microwave radar devices that
could be based on the new magnetron,
so he dropped his work on the klystron-
powered radar set, and devoted all His
energies to pulsed microwaves for the
next five years. But his klystron radar
could detect planes, as he demonstrated
to the “founding fathers” of the MIT
Radiation Laboratory in the winter of
1940 — in fact, it was the first working
radar set that any of us had ever seen.
But immediately after that demonstra-
tion, it was junked.

The Tizard Committee spent some
time in Tuxedo Park as guests of
Loomis, and on that occasion, he
brought a number of friends, including
Lawrence, into the newly formed Mi-
crowave Committee of the National
Defense Research Committee, which
had just been established by President
Roosevelt on the advice of Vannevar
Bush. Loomis was chairman of the

BIOGRAPHY

205

Committee, which took the responsibil-
ity for establishing the MIT Radiation
Laboratory, one of the world’s most
successful scientific and engineering
undertakings. Loomis made the ar-
rangements with industry for equip-
ping the laboratory with the necessary
hardware to make several flyable
night-fighter intercept radar sets, and
Lawrence took the responsibility of
staffing the laboratory, mostly with
young nuclear physicists. (The Tizard
Mission suggested this because the
British had found nuclear physicists to
be more quickly adaptable to a radical-
ly new set of “ground rules” than were
professional radio engineers.) Law-
rence persuaded Lee DuBridge to be-
come the director of the new labora-
tory, and that was a most fortunate
choice. He also traveled all over the
country, recruiting his former students
and their colleagues from the cyclotron
laboratories they had modeled after his
own, and he didn’t spare his own
laboratory; Edwin McMillan, Winfield
Salisbury and I all rushed off to Cam-
bridge in November of 1940, and didn’t
return to Berkeley for five years.

But this is the story of Alfred Loomis,
and not that of his friends, nor of the
great laboratory he founded and guided
so successfully with a loose rein. So I
will single out from the many successes
of the laboratory only two projects, one
invented by Loomis and the other
invented by Lawrence Johnston and
me, but in which he played a key role.
The first was Loran (for Long Range
Navigation), which was of great impor-
tance during the war, and is still a
major navigational aid in use all over
the world. Loran is a pulsed, “hyperbo-
lic system,” and in its original form
made use of Loomis’s great store of
knowledge about accurate timekeep-
ing. In fact, the Loran concept of a
master station and two slave stations
can be traced to the Shortt clocks,
which had a master pendulum swing-
ing in a vacuum chamber, and a heavy-
duty pendulum “slaved” to it, oscillat-
ing in the air.

To obtain a navigational “fix” with
Loran requires the measurement of the
time difference in arrival of pulses
from two pairs of transmitting stations.
Each such time difference places the
observer on a particular hyperbola.
The observer’s position is fixed by the
intersection of two such hyperbolas,
each derived from signals originating
from a pair of long-wave transmitting
stations. It is common for a Loran fix
to derive from only three transmitters,
with the middle one serving as a
member of two different transmitter
pairs. All the wartime Loran stations
operated at the same radio frequency,
and different pairs of transmissions
were distinguished by characteristic
repetition rates for their pulses. The

techniques for separating the signals
and for measuring their differences in
arrival time were “state of the art” at
that time, but the problem of synchron-
izing the transmissions to within a
microsecond, at points hundreds of
miles apart, was a new one in radio
engineering. Loomis proposed the fol-
lowing solution: The central station
was to be the master station, and its
transmissions were timed from a
quartz crystal. The other stations also
used quartz crystals, but in addition,
monitored the arrival times of the
pulses from the master station. When
the operators noted that the arrival
time of the master pulses was drifting
from its correct value, relative to the
transmitting time at that particular
“slave station,” the phase of the slave’s
quartz crystal oscillator was changed to
bring the two stations back into proper
synchronization. This procedure was
able to bridge over periods when the
signals at one station “faded out,” and
it was also what made Loran a practical
system during World War II, rather
than an interesting idea that would
have to await the invention of cesium
beam clocks, which were introduced in
the 1950s.

The second project of interest in this
biographical sketch is Ground Con-
trolled Approach, the “radar talk-
down” system for landing planes in bad
weather. The basic idea behind GCA
came to me one day in the summer of
1941 as I watched the first microwave
fire-control radar track an airplane,
automatically, from the roof of MIT. It
occurred to me that if a radar set could
track a plane accurately enough in
range, azimuth and elevation to shoot
it down, it could use that same informa-
tion to give landing instructions to a
friendly plane caught up in bad
weather.

Starting from the simple concept, my
associates and I, with strong backing
from Loomis, showed that the tech-
nique would work if the radar set gave
angular information that was as reli-
able as the optical information we used
in our tests. We had to wait several
months for the radar set to become
available for landing tests, but in one
early demonstration, the radar did
track several planes successfully as
they executed their approach and land-
ing. But in the scheduled radar tests,
the equipment was found to be quite
unable to track planes near the ground;
it would suddenly break away from the
line of sight to the plane, and point
instead down at the image of the plane
that was reflected in the surface of the
ground.

At the conclusion of this disastrous
set of tests, Loomis invited me to have
dinner with him in his suite at the Ritz-
Carlton in Boston and he did an amaz-
ing job in restoring my morale, which

was at is lowest ever. He said, “We
both know that GCA is the only way
planes will be blind-landed in this war,
so we have to find some way to make it
work. I don’t want you to go home
tonight until we’re satisfied that you’ve
come up with a design that will do the
job.” We both contributed ideas to the
system that eventually worked, and
that involved a complete departure
from all previous antenna configura-
tions. I’m sure that had it not been for
Loomis’s actions that night, there
would have been no effective blind
landing system in World War II, and
many lives would have been lost un-
necessarily. I would have immersed
myself in the other interesting projects
that concerned me, and would soon
have forgotten my disappointment and
my embarrassment.

Loomis played another interesting
role in GCA by ordering ten preproduc-
tion models of the embryonic device we
had invented at the Ritz-Carlton from a
small radio company on the West
Coast. He did this for two reasons: in
the first place, the laboratory had
failed badly in transferring its first
airborne radar set to industry for
production. The industrial engineers
predictably developed a bad case of
NIH (Not Invented Here), and prompt-
ly decided that everything had to be re-
engineered. The final product came
out so late and was so heavy that it
never saw any action. Because of that
experience, Loomis and Rowan Gaither
(later the first president of the Ford
Foundation) set up the “Transition
Office,” whose job was to avoid just
such problems. Rowan became head of
the Transition Office, and GCA was
selected as the first test case of the new
technique. Its basic idea was that a
company would be selected to produce a
new radar set before the original ideas
had been worked out in any detail. The
chief engineer of the designated com-
pany, plus a few of his assistants, would
come to the laboratory and participate
in the design and testing of the new
device, as members of an MIT-com-
pany team. In this way, when they
returned to their factory to produce the
device, everything in it would be “our
ideas” and “our design.” The Transi-
tion Office was a spectacular success,
and in the process, Rowan Gaither
became extraordinarily close, personal-
ly, both to Loomis and me.

The second reason that Loomis or-
dered the ten preproduction sets, using
NDRC-OSRD funds, was that the Army
and Navy as well as the RAF had all
said, independently, that their pilots
would “never obey landing instructions
from someone sitting in comfort on the
ground,” and that they would continue
pressing for something like the ILS
(Instrument Landing System) that is
now in general use throughout the

Loomis at Schenectady about 1960 while
visiting Guy Suits at G. E. Research Labs.

world. Loomis was confident that as
soon as the three services saw GCA
work, they would immediately accept
it, and want working models to test,
“yesterday.”

After some very successful tests at
Washington National Airport, in which
high service officials watched pilots
land “under the hood,” when those
pilots had never even heard of the
system until after they were in the air,
there was a rush to order several
hundred GCA sets. When the three
services learned that NDRC had ten
sets almost built, they called a meeting
at the Pentagon to allocate them for
tests in this country and in England.
Loomis was invited, and he asked me
to sit in. Neither of us said a word as
the admirals, generals, and air mar-
shalls engaged in a horse-trading ses-
sion that ended up with all ten sets
allocated to the services, and none to
MIT or to the NDRC. The meeting
was about to break up when Loomis
said quietly, “Gentlemen, there seems
to be some misapprehension concern-
ing the ownership of these radar sets;
it is my understanding that they be-
long to NDRC, and I am here to
represent that organization.” His
training as a lawyer was immediately
apparent, and after he had shown in
his gentle manner that he held all the
cards, an allocation that was satisfac-
tory to all concerned was quickly
worked out. And NDRC even ended
up with one of its own GCA sets!

At the end of the war, Lawrence gave
this evaluation of Loomis’s contribu-
tion to radar:4

He had the vision and courage to
lead his committee as no other
man could have led it. He used his
wealth very effectively in the way
of entertaining the right people
and making things easy to accom-
plish. His prestige and persuasive-
ness helped break the patent jams
that held up radar development.
He exercised his tact and diploma-
cy to overcome all obstacles. He’s
that kind of man, I’ve never seen
him lose his temper or heard him
raise his voice. He steers a math-
ematically straight course and suc-
ceeds in having his own way by
force, logic and by being right. I
am perfectly sure that if Alfred
Loomis had not existed, radar de-
velopment would have been re-
tarded greatly, at an enormous
cost in American lives.

Loomis’s other important role during
the war is so little known that its only
mention in print is in a brief obituary
notice I wrote for physics today.5
Many authors have commented on the

remarkable lack of administrative
roadblocks experienced by the Army’s
Manhattan District, the builders of the
atomic bombs. In my opinion, this
smooth sailing was due in large part to
the mutual trust and respect that
Secretary of War Stimson and Loomis
had. Loomis was in effect Stimson’s
minister without portfolio to the scien-
tific leadership of the Manhattan Dis-
trict— his old friends Lawrence, Comp-
ton, Fermi, and Robert Oppenheimer.
Loomis maintained a hotel room in
Washington throughout the war, which
his friends used when they couldn’t
find other accommodations, and one of
the reasons for this was so that he could
be available to talk with the Secretary
on short notice. Loomis was also a
member of a small committee set up by
the Secretary to advise him concerning
the V-l and V-2 weapons being devel-
oped by the Germans, and just coming
to the attention of military intelli-
gence. At the committee’s sugestion,
the V-l menace was largely blunted by
a combination of the SCR-584 devel-
oped in Loomis’s laboratory, an ad-
vanced computer developed by the Bell
Telephone Laboratory, the proximity
fuses developed by Merle Tuve and his
associates working under NDRC spon-
sorship, and the Army’s anti-aircraft
guns. The V-2 rockets could not be
defended against, and the committee
recommended the only course of action
possible, and the one that was fol-

lowed— capture of the firing sites.

Later years

Toward the end of the war, Loomis
was able to relax for the first time in
five years, and he concurrently made
an important change in his personal
life. He and Ellen were divorced, and
he married Manette Seeldrayers Ho-
bart. They had an extraordinarily
happy time together during the final 32
years of Alfred’s life. His lifestyle
underwent a dramatic change from one
of multiple homes staffed by many
servants to a very simple one, in which
he and Manette cooked dinner every
evening in East Hampton, side by side
in the kitchen. Alfred designed a
special rolling cart that brought the
food to one end of the table, where he
and Manette sat opposite each other,
and served themselves from the cart. If
there were guests, the plates were
passed down each side of the table to
them, from the cart. This new style of
servantless elegance was written up in
a magazine devoted to “good living.”

Loomis’s principal scientific inter-
ests changed at this time from the
physical to the biological. As an exam-
ple, I’ve mentioned his contributions to
research on hydra. In that period, one
of the bathrooms in his Park Avenue
apartment was filled with petri dishes
containing hydra. Loomis spent hours
each day examining the hydra under a
microscope, and comparing his ebser-

BIOGRAPHY

207

vations with those of his son, Farney.
He and Farney organized small meet-
ings to which they invited specialists in
subjects about which they wished to
learn more. As in the old Loomis
Laboratory days, the invitations in-
cluded first-class round-trip transpor-
tation, plus luxurious living at the
resorts where the meetings were held.

Loomis enjoyed introducing his
scientific friends to the pleasures that
are normally known only to the very
wealthy. For many years, he and
Manette visited California each spring,
and invited several couples from Law-
rence’s laboratory to be their guests at
the Del Monte Lodge at Pebble Beach,
and to play golf at the Cypress Point
Golf Club. In later years, the Loomises
spent their winters in Jamaica, where
their friends were invited, a week at a
time, to share with their hosts the sun,
the beach, and good food and good
conversation. As often happens with

men as they grow older, Loomis’s circle
of closest friends shrank to those he
called “my other sons.” I was fortunate
to be included, along with John S.
Foster Jr, Walter O. Roberts, Ronald
Christie and Julius A. Stratton. Had
Lawrence and Rowan Gaither outlived
Alfred, they would have continued to
visit the Loomises each winter in Ja-
maica, as members of the “other sons.”

I can think of no better way to end
this biographical memoir than by quot-
ing myself5

For those of us who were fortunate
to know him well, he will be
remembered as a warm and wise
friend, always interested in learn-
ing new things. I was his guest for
three days in May of this year, and
what he most wanted to learn from
me concerned programming tricks
for the Hewlett-Packard model 65
hand-held computer that was his
constant companion. I think it

most fitting that my last visual
memories of this renaissance man,
whose life encompassed and con-
tributed much to the electronic
age, should have him operating a
hand-held electronic computer
containing tens of thousands of
transistors.

* * *

This article was adapted from Biographical

Memoirs 51, The National Academy of

Sciences (1980).

References

1. W. B. Seabrook, Dr. Wood, Modern Wiz-
ard of the Laboratory, New York, Har-
court, Brace, New York (1941), page 213.

2. Ibid, page 221

3. E. N. Harvey, A. L. Loomis, Science 72, 42
(1930).

4. "Amateur of the Sciences,” Fortune,

March 1946, page 132.

5. L. W. Alvarez, physics today, November

1975, page 84. □

208

HISTORY OF PHYSICS

Harold Urey aid the
discovery of deuterium

Chemistry, nuclear physics, spectroscopy and

thermodynamics came together to predict and detect heavy hydrogen
before the neutron was known.

Ferdinand G. Brickwedde

It was on Thanksgiving day in 1931
that Harold Clayton Urey found defini-
tive evidence of a heavy isotope of
hydrogen. Urey’s discovery of deuter-
ium is a story of the fruitful use of
primitive nuclear and thermodynamic
models. But it is also a story of missed
opportunity and errors — errors that
are particularly interesting because of
the crucial positive role that some of
them played in the discovery. A look at
the nature of the theoretical and ex-
perimental work that led to the detec-
tion of hydrogen of mass 2 reveals
much about the way physics and chem-
istry were done half a century ago.

Although George M. Murphy and I
coauthored with Urey the papers1-3
reporting the discovery, it was Urey
who proposed, planned and directed
the investigation. Appropriately, the
Nobel Prize for finding a heavy isotope
of hydrogen went to Urey.

In this article we will look first at the
research that led to the discovery, as
that work was understood at the time.
Then we will look at some of the same
activity with the understanding that
only hindsight can give. Throughout
the discussion I will include fragments
from my memory — illustrative epi-
sodes connected with the discovery.

Urey’s career

Urey died last year at 87 years of age,
after a remarkably productive and in-
teresting life. He was a chemist with
very broad interests in science, remi-
niscent of the natural philosophers of
the eighteenth and nineteenth centur-
ies. Murphy4, who went on to become
professor and head of the department
of chemistry at New York University,
died in 1968.

Urey was born on a farm in Indiana
in 1893, and in childhood moved with

Ferdinand G. Brickwedde is Evan Pugh Re-
search Professor of Physics emeritus at Penn-
sylvania State University, in University Park,
Pennsylvania.

his family to a homestead in Montana.
After graduating from high school, he
taught for three years in public schools,
and then entered Montana State Uni-
versity as a zoology major and chemis-
try minor. Money was tight for him as
a college student. During the academic
year he slept and studied in a tent.
During his summers he worked on a
road gang laying railroad track in the
Northwest.

Urey graduated with a BS degree in
1917, when there was a need for chem-
ists in the war effort. He worked for
the Barrett Chemical Company in
Philadelphia on war materials. After
the war, Urey taught chemistry for two
years at Montana State University,
and in 1921 entered the University of
California at Berkeley as a graduate
student in chemistry, working under
the guidance of the renowned chemical
thermodynamicist Gilbert N. Lewis.
As a graduate student, Urey was a
pioneer in the calculation of thermo-
dynamic properties from spectroscopic
data. He received a PhD in 1923 and
spent the next academic year as an
American-Scandinavian Foundation
Fellow in the Physical Institute of
Niels Bohr in Copenhagen.

After Copenhagen, Urey joined the
faculty at Johns Hopkins University.
Although in the chemistry department,
he attended the physics department’s
regular weekly “journal” meetings for
faculty and graduate students, and he
participated in the discussions. It was
at these meetings that I, as a graduate
student in physics, became acquainted
with Urey. While Urey was at Hopkins,
he and Arthur E. Ruark coauthored the
classic textbook, A toms. Molecules, and
Quanta, which was the first comprehen-
sive text on atomic structure written in
English. I proofread the entire book in
galley for the authors.

Urey’s work bridged chemistry and
physics. In 1929 he was appointed
associate professor of chemistry at Co-
lumbia University, and from 1933 to

PHYSICS TODAY / SEPTEMBER 1982

1940 he was the founding editor of the
American Institute of Physics publica-
tion, Journal of Chemical Physics.
When the biographical publication
“American Men of Science” took note
of scientists selected for recognition by
their peers, Urey was elected in phy-
sics. In 1934 — only three years after
the discovery of deuterium — Urey was
awarded the Nobel Prize in chemistry.

Before the search

In 1913, Arthur B. Lamb and Richard
Edwin Lee, working at New York Uni-
versity, reported5 a very precise mea-
surement of the density of pure water.
Their measurements were sensitive to
2xl0-7 g/cm3. Various samples of
water, which were carefully prepared
using the best purification techniques
and temperature controls, varied in
density by as much as 8xl0-7 g/cm3.
They concluded that pure water does
not possess a unique density.

Today we know that water varies in
isotopic composition, and that samples
of water with different isotopic compo-
sitions have different vapor pressures,
making distillation a fractionating pro-
cess. The Lamb-Lee investigation is
interesting because it was the first
reported experiment in which an isoto-
pic difference in properties was clearly
in evidence. It is the earliest recogniz-
able experimental evidence for iso-
topes. (The existence of isotopes was
proposed independently by Frederick
Soddy, in England, and by Kasimir
Fajans, in Germany, in 1913.) Think
what the result might have been had
Lamb and Lee pursued a progressive
fractionation of water by distillation
and separated natural water into frac-
tions with different molecular weights.

Less than two decades later, by the
time of the discovery of deuterium,
isotopes were an active field of re-
search. The rapid development of nu-
clear physics after 1930 was initiated
by isotope research. It was a time of
search for as-yet undiscovered isotopes,

BIOGRAPHY

209

especially of the light elements, hydro-
gen included, and Urey was very much
a participant.

I remember a conversation in 1929
with Urey and Joel Hildebrand, a fam-
ous professor of chemistry at Berkeley.
It took place during a taxi ride between
their hotel and the conference center
for a scientific meeting we were attend-
ing in Washington. When Urey asked
Hildebrand what was new in research
at Berkeley, Hildebrand replied that
William Giauque and Herrick John-
ston had just discovered that oxygen
has isotopes with atomic weights 17
and 18, the isotope of weight 18 being
the more abundant. Their paper6
would appear shortly in the Journal of
the American Chemical Society. Then
Hildebrand added, “They could not
have found isotopes in a more impor-
tant element.” Urey responded: “No,
not unless it was hydrogen.” This was
two years before the discovery of deu-
terium. Urey did not remember this
remark, but I did.

At the time, answers were being
sought to questions such as: Why do

isotopes exist, and what determines
their number, relative abundances and
masses (packing fractions)?

Urey, along with others, constructed
charts of the known isotopes to show
relationships bearing on their exis-
tence. The figure on page 36 is one of
Urey’s charts. At the time, the neutron
had not been discovered — it was disco-
vered in 1932, the year after deuter-
ium. The chart was based on the the-
ory that atomic nuclei were composed
of protons, plotted here as ordinates,
and nuclear electrons, plotted as abscis-
sae— the number of protons was the
nuclear mass number, and the number
of nuclear electrons was the number of
protons minus the atomic number of
the element. In Urey’s chart, the filled
circles represent the nuclei from H1 to
Si30 that were known to exist before
1931. The open circles represent nuclei
unknown before 1931. The chart’s pat-
tern of staggered lines, when extended
down to H1, suggested to Urey that the
atoms H2, H3 and He5 might exist
because they are needed to complete
the pattern.

Urey had a copy of this chart hang-
ing on a wall of his laboratory. The
isotope helium-5 does not exist, and the
staggered line does not provide a place
for the isotope helium-3, which was
discovered later. The diagram is only
of historical interest now, but it was an
incentive to Urey to look for a heavy
isotope of hydrogen.

Prediction and evidence

In 1931 — the year of the discovery of
deuterium — Raymond T. Birge, a pro-
fessor of physics at the University of
California, Berkeley, and Donald H.
Menzel, professor of astrophysics at
Lick Observatory, published7 a letter to
the editor in Physical Review on the
relative abundances of the oxygen iso-
topes in relation to the two systems of
atomic weights that were then in use —
the physical system and the chemical
system. Atomic weights in the physical
system were determined with the mass
spectrograph and were based on setting
the atomic weight of the isotope O' 6 at
exactly 16. In the chemical system,
atomic weights were determined by

Harold Clayton Urey and a country schoolhouse in Indiana where he taught
after graduating from high school. Urey taught for three years in public schools
in Indiana and Montana before he entered Montana State University.
(Schoolhouse photo from the Urey collection, AIP Niels Bohr Library.)

210

HISTORY OF PHYSICS

bulk techniques, and the values were
based on setting at 16 the atomic
weight of the naturally occurring mix-
ture of oxygen isotopes, O16, O17 and
O18. Thus the atomic weights of a
single isotope or element on the two
scales should differ. The weight
numbers should be greater on the phys-
ical scale.

However, in 1931 the atomic weights
of hydrogen on the two scales were the
same within the claimed experimental
errors. The chemical value was
1.00777 + 0.00002. The mass-spectro-
graphic value, determined by Francis
W. Aston of the Cavendish Laboratory,
was 1.00778 + 0.00015. Birge and
Menzel pointed out that the near coin-
cidence of these two atomic weights
leads to the conclusion that normal
hydrogen is a mixture of isotopes — H1
in high concentration and a heavy iso-
tope in low concentration. The atomic
weight was not higher on the physical
scale because the mass-spectroscopic
techniques saw only the light isotope.

To the heavy isotope they gave the
symbol H2, perhaps the first time this
symbol occurred in the literature. As-
suming the atomic weight of heavy
hydrogen to be two, Birge and Menzel
calculated its relative abundance from
the supposed equivalence of the atomic
weights of hydrogen-1 on the physical
scale and the normal mixture of hydro-
gen isotopes on the chemical scale.
They obtained 1/4500 for the abun-
dance of H2 relative to H1.

Within a day or two at most after
receiving the 1 July 1931 issue of the
Physical Review, Urey proposed and
planned an investigation to determine
if a heavy isotope of hydrogen did really
exist.

Urey and Murphy, working at Co-
lumbia, identified hydrogen and its iso-
tope spectroscopically, using the
Balmer series lines. The atomic spec-
trum was produced with a Wood’s elec-
tric discharge tube operated in the so-
called black stage — the configuration
of current and pressure that most
strongly excites hydrogen’s atomic
spectrum relative to its molecular spec-
trum. They observed the spectra with
a 21-foot grating, in the second order.
The dispersion was 1.3 A per mm. The
expected shifts, then, were of the order
of 1 mm, as the numbers in the table
indicate. The vacuum wavelengths of
deuterium’s lines were calculated us-
ing the Balmer series formula

1/J„ = i?H(l/22 - 1 /n2) (1)

n = 3, 4, 5, . . .

■ffH =(2 Ti2e4/h3c)memH/(me + mH)

and the “best” values for the atomic
constants. The Balmer a-lines of hy-
drogen and deuterium are separated by
1.8 A, the /8-lines by 1.3 A, and the y-
lines by 1.2 A. The concentrations of
deuterium relative to hydrogen are de-

NUCLEAR ELECTRONS

Protons versus “nuclear electrons” for

atomic nuclei from H1 to Si30. The plot shows a
pattern that led Urey to look for a heavy
isotope of hydrogen. Open circles represent
nuclei that were unknown in 1931, when the
chart was produced.

termined by comparing the measured
times required to produce plate lines of
H and D of equal photographic densi-
ties. The exposure times for H/7 and H y
were about 1 second.

Using cylinder hydrogen, Urey and
Murphy found very faint lines at the
calculated positions for D/J, D y and D<5.
The lines were faint because of the low
concentration of deuterium in normal
hydrogen. There was a possibility that
the new lines arose from impurities, or
were grating ghost lines arising from
the relatively intense hydrogen Balmer
spectrum.

Clinching evidence

Urey decided not to rush into print to
stake a claim to priority in this impor-
tant discovery; he decided to postpone
publication until he had conclusive evi-
dence that the “new” spectral lines
attributed to the heavy isotope were
authentic and not impurity or ghost
lines. This evidence could be obtained
by increasing the deuterium concentra-
tion in the hydrogen filling the Wood’s
tube and looking for an increase in
intensity of the deuterium Balmer lines
relative to the hydrogen Balmer lines.

After careful consideration of differ-
ent methods for increasing the deuter-
ium concentration, Urey decided on a
distillation that would make use of an
anticipated difference in the vapor
pressures of liquid H2 and liquid HD.
He made a statistical, thermodynamic
calculation of the vapor pressures of
solid H2 and solid HD at the triple point
of H2, 14 kelvins, where the liquid and
crystal phases of H2 are in equilibrium
and have the same vapor pressure. The
calculation was based on the Debye
theory of solids and the zero-point vi-
brational energy of the solid, 9R9/8 in
the Debye notation. At 14 K, the calcu-
lated ratio of vapor pressures, P(HD)/
P(H2), is 0.4, indicating a large differ-

ence in the vapor pressures of solid H2
and HD. On this basis Urey expected a
sizeable difference in the vapor pres-
sures of liquid H2 and HD at 20.4 K, the
boiling point of H2.

Urey approached me at the National
Bureau of Standards in Washington,
inviting me to join the search for a
heavy isotope of hydrogen by evaporat-
ing 5- to 6-liter quantities of liquid
hydrogen to a residue of 2 cm3 of liquid,
which would be evaporated into glass
flasks and sent by Railway Express to
Columbia University for spectroscopic
examination. At the time, 1931, there
were only two laboratories in the Unit-
ed States where liquid hydrogen was
available in 5- or 6-liter quantities.
One was the National Bureau of Stan-
dards in Washington and the other was
Giauque’s laboratory at the University
of California, Berkeley. I was happy to
cooperate, and I prepared — by distill-
ing liquid hydrogen at the Bureau of
Standards — the samples of gas in
which the heavy isotope was identified.

The first sample I sent to Urey was
evaporated at 20 K and a pressure of
one atmosphere. It showed no appre-
ciable increase in intensity of the spec-
tral lines attributed to heavy hydrogen.
This was unexpected.

The next samples were evaporated at
a lower temperature — 14 K at 53 mm of
mercury pressure, the triple point of
H2 — where the relative difference in
the vapor pressures of H2 and HD was
expected to be larger than at 20 K, and
the rate at which heavy hydrogen is
concentrated was expected to be more
rapid.

These samples showed 6- or 7-fold
increases in the intensities of the
Balmer lines of deuterium. On this
basis, it could be concluded that the
lines in the normal hydrogen spectrum
attributed to deuterium were really
deuterium lines, but the clinching evi-
dence was finding that the photograph-
ic image of the Da line — the most
intense D-Balmer line — was a partially
split doublet as predicted by theory for
the Balmer series spectrum.

From measurements of the relative
intensities of the H and D Balmer
series lines, Urey estimated that there
was one heavy atom per 4500 light
atoms in normal hydrogen. Later mea-
surements showed it to be nearer one in
6500.

Unraveling a comedy of errors

It is now clear why the first distilled
hydrogen sent to Urey did not show the
expected increase in the deuterium
concentration, and maybe even showed

News story on the awarding of the 1934
Nobel Prize in chemistry. Article appeared 16
November 1 934. (Copyright The New York
Times. Reprinted by permission.)

BIOGRAPHY

211

Calculated Balmer series wavelengths

Ai(H’ - D)

Line

i(H’)

(A)

i(D)

(A)

calculated

(A)

observed

(A)

a

6564.686

6562.899

1.787

1.79

0

4862.730

4861.407

1.323

1.33

r

4341.723

4340.541

1.182

1.19

s

4102.929

4101.812

1.117

1.12

These values were calculated using equation 1 with MH = 1.007775 g, MD = 2.01363 g,
me = 5.491 x10 4 g and RH = 109677.759 cm V

a small decrease. The explanation
came with the discovery of the electro-
lytic method for separating H and D,
suggested by Edward W. Washburn,
chief chemist at the National Bureau of
Standards, and verified8 experimental-
ly by Washburn and Urey just after the
publication of our April 1932 paper.3

When Urey considered different
methods for concentrating deuterium,
he included the electrolytic method,
and discussed it with Victor LaMer, a
colleague at Columbia, and a world
authority on electrochemistry. LaMer
was so discouraging about success in
separating hydrogen isotopes by elec-
trolysis that Urey abandoned the elec-
trolytic method and adopted the distil-
lation method. LaMer reasoned that
the differences in equilibrium concen-
trations of isotopes at the electrodes of
a cell at room temperature would be
very small and hence a fractionation of
the isotopes would be negligible.

Washburn viewed the situation dif-
ferently. He pointed to the large rela-
tive difference in atomic weights of the
hydrogen isotopes — a relative differ-
ence that is much larger for the hydro-
gen isotopes than for the isotopes of any
other element. Hence, thought Wash-

burn, the hydrogen isotopes might be-
have differently from the isotopes of
other elements.

Washburn, the empiricist, was right;
the isotopes of hydrogen are separated
relatively easily by electrolysis, but
this was not realized until after the
discovery of deuterium.

The hydrogen we liquefied and dis-
tilled for Urey was generated electroly-
tically. Before preparing the first sam-
ple for Urey, the electrolytic generator
was completely dismantled, cleaned
and filled with a freshly prepared solu-
tion of sodium hydroxide. Because deu-
terium becomes concentrated in the
electrolyte in the generator, the first
gaseous hydrogen to be discharged was

deficient in deuterium. The concentra-
tion of deuterium in the hydrogen
evolved was about one sixth the concen-
tration of deuterium in the electrolyte,
and hence about one sixth the concen-
tration of deuterium in normal hydro-
gen. Distillation of the deuterium-defi-
cient liquid hydrogen increased the
concentration of D relative to H and
restored in the first sample approxi-
mately the original concentration of
deuterium in normal hydrogen.

As electrolysis progressed, water was
added to replace that which was con-
sumed. The concentration of deuter-
ium in the electrolyte increased to the
point where the rate at which deuter-
ium left the generator balanced the
rate at which it arrived in the added
water. Hence, after the electrolytic
generator had been in use for some
time, there was a dynamic equilibrium;
so the hydrogen evolved from the gen-
erator for our second and third samples
for Urey had approximately the nor-
mal concentration of deuterium.
When we liquefied this hydrogen and
evaporated 5 or 6 liters down to 2 cm3,
the concentration of deuterium in the
residue was increased by a factor of
about six.

Here we lower the curtain on a “com-
edy of errors” — LaMer’s error of not
understanding better the principles
that govern isotopic fractionation dur-
ing electrolysis, and my error of attrib-
uting to sloppy technique our failure to
effect an increase of deuterium concen-
tration in the first sample we sent to
Urey. Had I analyzed our part of the
process, I think we might have disco-
vered the electrolytic concentration of
deuterium. Had LaMer been more
knowledgeable, Urey would have made
his own concentration of deuterium
electrolytically and I should have had
no part in the discovery of deuterium.

Reporting the result

After the discovery of deuterium,
Urey faced a very practical problem in
reporting it — a problem characteristic
of the status of research before World
War II. Urey’s research at Columbia,
and ours at the National Bureau of
Standards, where I was chief of the low
temperature laboratory, was carried
out without the support of any govern-
ment research grant. It was said that

NOBEL AWARD GOES

Columbia Scientist Gets the
1934 Chemistry Prize for
Discovering ‘Heavy Water.’

ACHIEVEMENT WAS HAILED

Seen as of Especial Value in
Cancer Study — Has Proved
Great Spur to Research.

Wireless to The New York Time*.

STOCKHOLM, Nov. 15.-The
Nobel Prize in Chemistry for 1934
was awarded today to Professor
Harold C. Urey of Columbia Uni-
versity because of his discovery of
“heavy water.”

The chemistry prize for 1933 will
not be awarded. It was also an-
nounced that there would be no
prize in physics for this year.

Achievement Was Hailed.

Dr. Harold Clayton Urey won a
position in the forefront among
scientists by his discovery of “heavy
water,” which has been hailed by
scientists the world over as ranking j
among the great achievements of j
modern' science.

The Willard Gib Mede’

Chicago section
Chernies’

Dr. T

Ossij) oarber otui.ios.

WINS NOBEL PRIZE.

Professor Harold Urey.

DEFENSE TO SUBPOENA
LINDBERGH FOR TRIAL

Betty Gow Also to Be Summoned
as Witness — Fight Planned to
Release Hauptmann Funds.

Special to The New York Times.
FLEMINGTON, N. J., Nov. 15.-
Colonel Charles a. Lindbergh and
Betty Gow, wh *•» fir-»t son’s

'urse, will ' de

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212

HISTORY OF PHYSICS

Mass spectrometer with Urey at the controls, after the discovery of deuterium. (Photograph
courtesy of King Features Syndicate.)

research in that period was done with
string and sealing wax; it was in fact
done mostly with homemade appara-
tus. The US government policy of
grants in support of research dates
from a later time — from World War II.

Before the War it was a problem to
find funds for travel to scientific meet-
ings. I received a telephone call from
Urey, telling me that it appeared he
was not going to get funds to travel to
the December 1931 American Physical
Society meeting at Tulane University,
where he planned to present a paper
reporting the discovery of deuterium.
He asked me if I could get travel funds
and present the paper. For this I had to
see Lyman J. Briggs, assistant director
of research and testing at the Bureau of
Standards. Briggs, soon to be named
NBS director, was an understanding
and considerate physicist who, on
learning of the work to be reported,
made funds available for my travel. In
the meantime, Bergen Davis, a promi-
nent physicist at Columbia, heard of
Urey’s problem and went to see Colum-
bia president Nicholas Murray Butler,
who made funds available for Urey’s
travel. So we both went to Tulane for
the APS meeting, and Urey presented
the ten-minute paper.' Over the next
few months we published more detail
in a letter2 to the editor and a full-
length paper3 in Physical Review.

I remember asking Birge at a later
APS meeting why he and Giauque had
not followed up on his prediction7 of the
existence of heavy hydrogen. They
might have demonstrated the existence
of deuterium by concentrating the
heavy isotope through distillation of a
large quantity of liquid hydrogen as
Urey and I had done. Giauque had a
very fine, large-capacity hydrogen liq-
uefier suitable for this. Birge’s reply
was that he was busily engaged on
other important work that demanded
his attention. When I told Urey of this
discussion, his comment was: “What in
the world could Birge have been work-
ing on that was so important?”

Apropos of the above, I quote here
from a letter of 6 May 1981 from Robert
W. Birge, son of Raymond T. Birge, and
also a physicist:

After reading some more about my
father’s life, I think I know why he
didn’t try to concentrate deuter-
ium. I believe he was an analyst
more than a hardware builder and
it probably never occurred to him
to do it that way. He said that at
the time several people were try-
ing to see the deuterium lines in
spectra, but they [Urey, Brick-
wedde and Murphy] did it first.
But as you know, the important
point was that Urey realized that
[the concentration of] deuterium
could be enhanced.

The two men remained friends

throughout their lifetime.

Frederick Soddy, the English che-
mist who received the 1921 Nobel Prize
in Chemistry for discovering the pheno-
menon of isotopy, did not accept the
notion that deuterium was an isotope of
hydrogen. Soddy worked with isotopes
of the naturally radioactive elements,
whose atomic weights are large and
whose isotopic relative mass differ-
ences are small. These isotopes showed
no observable differences in chemical
properties and were inseparable chemi-
cally. When Soddy coined the word
isotope he gave it a definition that
included chemical inseparability of iso-
topic species of the same element. This
was generally accepted before the dis-
covery of the neutron in 1932.

After the discovery of the neutron,
isotopes were defined as atomic species
having the same number of protons in
their nuclei but different numbers of
neutrons. But Soddy stuck to chemical
inseparability as a criterion for iso-
topes and therefore refused to recog-
nize deuterium as an isotope of hydro-
gen. For Soddy, deuterium was a
species of hydrogen, with different
atomic weight, but not an isotope of
hydrogen.

A fortunate mistake

Four years after the discovery of
deuterium, Aston reported9 an error in

his earlier mass-spectrographic value
of 1.00778 for the atomic weight of
hydrogen-1 on the physical scale — the
value used by Birge and Menzel in their
1931 letter.' The revised value on the
physical scale was 1.00813, which cor-
responds to 1.0078 on the chemical
scale, in agreement with the then cur-
rent value for the atomic weight of
hydrogen (1.00777) on the chemical
scale. There was then no need or place
for a heavy isotope of hydrogen. The
conclusion of Birge and Menzel was
thus rendered invalid. Indeed, on the
basis of Aston’s revised value, Birge
and Menzel would have been obliged to
conclude that, if anything, there was a
lighter — not a heavier — isotope of hy-
drogen.

The prediction of Birge and Menzel
of a heavy isotope of hydrogen was
based on two incorrect values for the
atomic weight of hydrogen, namely As-
ton’s mass-spectrographic value and
the chemical value, which also should
have been greater. We are obliged to
conclude that the experimental error
in the determination of the atomic
weights exceeded the difference in the
atomic weights on the two scales.

Urey was not aware of this when he
planned his experiment. It was not
until 1935 when Urey’s Nobel lecture
was in proof that Aston published his
revised value. Urey added the follow-

BIOGRAPHY

213

ing to the printed Nobel lecture:

Addendum

Since this [Nobel lecture10] was
written, Aston has revised his
mass-spectrographic atomic
weight of hydrogen (H) to 1.0081
instead of 1.0078. With this mass
for hydrogen, the argument by
Birge and Menzel is invalid. How-
ever, I prefer to allow the argu-
ment of this paragraph [the third
paragraph of Urey’s Nobel lecture]
to stand, even though it now ap-
pears incorrect, because this pre-
diction was of importance in the
discovery of deuterium. Without
it, it is probable we would not have
made a search for it and the discov-
ery of deuterium might have been
delayed for some time.

Needless to say, Urey and his collea-
gues were very glad that an error of
this kind had been made. Aston said
that he did not know what the moral of
it all was. He would hardly advise
people to make mistakes intentionally,
and he thought perhaps the only thing
to do was to keep on working.

Impact of the discovery

It has been said that Nobel prizes in
physics and chemistry are awarded for
work, experimental or theoretical, that
has made a significant change in ongo-
ing work and thinking in science. The
announcement that Urey was chosen
as the 1934 laureate in chemistry came
less than three years after that ten-
minute paper in New Orleans announc-
ing the discovery of deuterium. This
uncommonly early award followed a
spectacular display in deuterium-relat-
ed research. In the first two-year peri-
od following the discovery, more than
100 research papers were published on
or related to deuterium and its chemi-
cal compounds, including heavy water.
And there were more than a hundred
more11 in the next year, 1934.

The use of deuterium as a tracer
made it possible to follow the course of
chemical reactions involving hydrogen.
This was especially fruitful in investi-
gations of complex physiological pro-
cesses and in medical chemistry, as in
the breakdown of fatty tissue and in
cholesterol metabolism.

Also, the discovery of heavy hydro-
gen provided a new projectile, the deu-
teron, for nuclear bombardment ex-
periments. The deuteron proved
markedly efficient in disintegrating a
number of light nuclei in novel ways.
As the deuteron, with one proton and
one neutron, is the simplest compound
nucleus, studies of its structure and of
its proton-neutron interaction took on
fundamental importance for nuclear
physics.

Many of the early research papers
dealt with isotopic differences in phys-
ical and chemical properties. Theories
developed for the atomic mass depen-
dence of physical and chemical proper-
ties were tested experimentally. These
investigations were especially interest-
ing because, before the discovery of
deuterium, chemical properties were
generally supposed to be determined by
the number and configuration of the
extranuclear electrons, quantities that
are identical for isotopes of the same
element. It had not been realized that
chemical properties are also affected —
but to a lesser degree — by the mass of
the nucleus.

In thinking about Urey’s search for
deuterium, beginning with his early
diagram of the isotopes, I am reminded
of the Greek inscription on the facade
of the National Academy of Sciences
building in Washington, taken from
Aristotle:

The search for truth is in one way
hard and in another easy, for it is
evident that no one can master it
fully or miss it wholly. But each
adds a little to our knowledge of

nature, and from all the facts as-
sembled there arises a certain
grandeur.

* * *

I wish to acknowledge the valuable assis-
tance of my wife, Langhorne Howard Brick-
wedde, especially for her help in recalling
incidents of the early thirties connected with
the discovery of deuterium. This article is
based on a paper I presented 22 April 1981 in
Baltimore, Maryland, at the inaugural ses-
sion of the American Physical Society’s Divi-
sion of History of Physics.

References

1. The thirty-third annual meeting of the
American Physical Society at Tulane
University, 29-30 December 1931. Ab-
stracts of papers presented: Phys. Rev.
39, 854. Urey, Brickwedde and Murphy
abstract #34.

2. H. C. Urey, F. G. Brickwedde, G. M.
Murphy, Phys. Rev. 39, 164 (1932).

3. H. C. Urey, F. G. Brickwedde, G. M.
Murphy, Phys. Rev. 40, 1 (April 1932).

4. For an interesting account of the discov-
ery of deuterium, see G. M. Murphy,
“The discovery of deuterium,” in Isoto-
pic and Cosmic Chemistry, H. Craig, S. L.
Miller, G. J. Wasserburg, eds., North-
Holland, Amsterdam (1964). (Dedicated
to Urey on his seventieth birthday.)

5. A. B. Lamb, R. E. Lee, J. Am. Chem. Soc.
35, part 2, 1666 (1913).

6. W. F. Giauque, H. L. Johnston, J. Am.
Chem. Soc. 51, 1436, 3528 (1929).

7. R. T. Birge, D. H. Menzel, Phys. Rev. 37,
1669 (1931).

8. E. W. Washburn, H. C. Urey, Proc. Nat.
Acad. Sci. US 18, 496 (1932).

9. F. W. Aston, Nature 135, 541 (1935);
Science 82, 235 (1935).

10. H. Urey in Nobel Lectures in Chemistry,
1922-1941, published for the Nobel
Foundation by Elsevier, Amsterdam
(1966).

11. Industrial and Engineering Chemistry,

News Edition 12, 11 (1934). □

Despite years of working under

house arrest in his native land, Kapitza has remained

the outspoken dean of Soviet science.

Grace Marmor Spruch physics today / September 1979

Pyotr Kapitza, octogenarian
dissident

Four of the five Soviet academicians at-
tending a Pugwash Conference in 1973
had, earlier that year, signed a condemna-
tion of Andrei Sakharov for his political ut-
terances. The fifth, Pyotr L. Kapitza, had
not signed. Kapitza — the dean of Soviet
science, winner of two Stalin prizes, four
times awarded the Order of Lenin and last
year awarded the Nobel Prize — had pre-
viously played Sakharov’s role as the most
outspoken Soviet scientist. In fact, he was
also thought to have played Sakharov’s
role as father of the Soviet H bomb. Nobel
Laureates are usually known solely for
their work; a small number, however, are
known as much for their personalities

or the circumstances under which they
worked. Kapitza is one of the latter.
Most scientists have seen abstracts of his
life, but few are familiar with the entire
article.

The early years

Kapitza was born in 1894 in Kronstadt,
famous as the site of a sailors’ uprising in
1921. His father was a general in the
tsarist army engineering corps (said to
have worked on the defenses of Kron-
stadt), and his mother was the daughter
of a general. Kapitza received his sec-
ondary school education in Kronstadt and
electrical-engineering training at the

Petrograd Polytechnical Institute. After
his graduation in 1918, he stayed on as a
lecturer at Petrograd and by the time he
left for England in 1921, had six scientific
papers to his credit.

Kapitza arrived in England at age
twenty-seven — thin, unhappy, unknown,
looking like “a tragic Russian prince,”
according to Cambridge don G. Kitson
Clark. Kapitza’s native country lay rent
by civil war, disease and famine, his wife
and two small children victims. In ex-
treme depression, he had left on the rec-
ommendation of the eminent scientist
Abram F. Ioffe and, it is said, the inter-
cession of writer Maxim Gorky, as part of

an official Soviet delegation to the UK.

In England Kapitza made for Cam-
bridge and the Cavendish Laboratory,
headed at that time by Ernest Ruther-
ford. The story is told that Kapitza asked
to work in the Cavendish as a research
student but was told by Rutherford that
there were no openings. Kapitza in-
quired about the accuracy of Rutherford’s
measurements and was told it was roughly
ten per cent. Kapitza then pointed out
that one additional student was less than
ten per cent of the total of thirty and that
Rutherford would be within the limits of
his experimental error if he accepted
him — which Rutherford did. (There is a
“second-order” error here in that some
versions of the incident have Rutherford
stating three per cent as his experimental
error — in which case Kapitza ’s entry into
the Cavendish was a tighter squeeze.)

The ancedote illustrates the character
of both men and the relationship that was
to develop between them. Kapitza had
a chutspah and vitality seldom found in
Englishmen, and Rutherford, no En-
glishman himself but a New Zealander — a
loud, brusque, “Colonial” — responded.

Kapitza’s letters

Not everyone responded positively to
Kapitza. One Englishman, offering ob-
jective criteria by which to assess Kapit-
za’s character, recommended I read letters
Kapitza had written to his mother during
his early days in Cambridge. These, in a

Grace Marmor Spruch is professor of physics at
the Newark Campus of Rutgers University.

Russian biography of Rutherford, would
show Kapitza’s “Napoleonic ambition.”
W. H. Auden once wrote:

... to me, at least, who was born and
bred a British Pharisee, Russians are
not quite like other folk. If their re-
spective literatures in the nineteenth
century are a guide, no two sensibilities
could be more poles apart than the
Russian and the British . . . Time and
time again, when reading the greatest
Russian writers, like Tolstoy and Dos-
toievsky, I find myself exclaiming, “My
God, this man is bonkers!”

I read the letters, and to me, at least, an
American of Russian descent, though they
seemed somewhat Oedipal, they were
within the bounds of normal boasting to
one’s mother.

Dated every few days at first, the letters
overflow with terms of endearment and
concern over how his mother will get along
without him. (According to a British
woman who met her years later, Kapitza’s
mother, a collector of folklore and writer
of children’s stories, was an intelligent,
capable woman who gave the impression
she could more than cope.) The letters
tremble with Kapitza’s own insecurity.
He fears that inadequate knowledge of
English hampers him in the expression of
ideas and writes that even in Russian he
expresses himself poorly. He refers to his
manners as crude.

The interval between letters becomes
longer and the mood more confident as he
gets more involved in his work. After
three months in the laboratory he
writes:

The famous crocodile marks the entrance
to the Royal Society Mond Laboratory in
Cambridge. Sculptor Eric Gill carved the
design, on Kapitza's commission, for the
opening of the laboratory in 1933. During
the following year Kapitza was detained while
on a visit to the Soviet Union, and he was
not allowed to leave the country until 1966.
The photographs to the right and left show
him in 1937 and during the 1960’s.

. . .Rutherford is increasingly aimiable
to me . . . But I am somewhat afraid of
him. I work right next door to his of-
fice. This is bad, as I must be careful
about smoking. If he should see me
with a pipe in my mouth, there would
be trouble. But thank God he has a
heavy step, and I can distinguish it
from others . . .

In the next letter Kapitza calls Ruth-
erford “Crocodile.” (One is tempted to
associate Rutherford’s heavy tread with
the ticking clock in Captain Hook’s croc-
odile, but Kapitza’s friends doubt that he
had read Peter Pan. )

The letters trace Kapitza’s progress and
tell of the increasing amount of space he
is occupying in the Cavendish, with so-
ciological comments interspersed:

. . . Englishmen get drunk easily. And
it is noticeable immediately. Their
features become lively and animated;
they lose their stoniness . . . Apparently
my Russian belly is better adapted to
alcohol than an English one.

Here — it’s funny — if the professor is
nice to you, it immediately affects ev-
eryone else in the laboratory; they also
show you consideration.

DAVID SCHOENBERG

216

HISTORY OF PHYSICS

The letters also relate Kapitza’s at-
tachment to his motorcycle and one in-
stance of his lack of attainment when he
and James Chadwick were sent flying,
Kapitza pointing out that it was Chad-
wick in the driver’s seat. Kapitza’s face
bore the brunt of the experience; it was so
swollen and discolored he was ashamed to
show it in the laboratory until informed
by a friend that at Cambridge such a face,
when associated with sport rather than
with alcohol, was considered chic.

About Rutherford he wrote:

You can’t imagine what a great and
wonderful man he is,
and about Rutherford’s solicitude for
him:

[it] must surely equal that from one’s
own father . . . his kindness to me is
boundless.

Although Auden might attribute some
of Kapitza’s statements to Russsian ef-
fusiveness, most scientists would agree
that Cambridge was “the world’s foremost
school,” and, if qualified by “experimen-
tal,” that Rutherford was “the world’s
foremost physicist and organizer.” In
addition, the letters cite facts that support
some effusions. For example, after re-
ceiving his PhD, Kapitza, effectively
“broke,” was lent money by Rutherford
with which to go away for a rest. Ruth-
erford also offered Kapitza the Clerk
Maxwell Prize, a three-year stipend nor-
mally awarded to the best young student
to help him through his degree, despite
Kapitza having already completed his
doctorate.

In the final letter of the group Kapitza
tells his mother that Rutherford has
asked him to stay on for about five years,
after which he could dictate his own terms
in seeking employment.

At the Cavendish

Kapitza started out in nuclear physics
at the Cavendish, but soon his natural
inclination toward engineering began to
assert itself. Some say engineering is his
real metier. (When he had enough
money to buy a new car, he would con-
sider only one for which the manufacturer
would supply a set of blueprints; Vauxhall
was the only company to comply.) Kap-
itza set to work on the problem of ob-
taining very strong magnetic fields for
investigations of atomic properties. He
sent much greater currents through the
coil of his electromagnet than the coil
could sustain — but for less time than it
would take the coil to burn out. Here
Kapitza utilized his engineering back-
ground in designing apparatus that would
permit currents of about 10 000 amperes
to be switched off after 0.01 second. He
wrote to Rutherford, then on vacation:
We managed to obtain fields over
270 000 [gauss] ... we could not go
further as the coil bursted with a great
bang . . . The power in the circuit was
about 13V2 kilowatts . . . approximately
three Cambridge supply stations con-

DAVID SCHOENBERG

The first flask of liquid helium made with
Kapitza’s liquefier at the Mond Laboratory, 1934.
Kapitza's inexpensive method for helium liq-
uefaction led to the Collins Liquefier.

nected together, but the result of the
explosion was only the noise, as no ap-
paratus has been damaged, except the
coil . . . The accident was the most in-
teresting of all the experiments ... as
we know exactly what has happened
when the coil bursted. We know just
what an arc of 13 000 amperes is like.
Apparently it is not at all harmful for
the apparatus and the machine, and
even for the experimenter if he is suf-
ficiently far away.

Kapitza began to put down roots in
Cambridge, within the limits any for-
eigner can put down roots in England and
within his own limits: He was a Soviet
citizen, and a loyal one. He became As-
sistant Director of Magnetic Research at
the Cavendish, a Fellow of Trinity College
and of the Royal Society, took to smoking
a special tobacco carried by a local Cam-
bridge tobacconist, and made some deep,
enduring friendships.

One such friendship was with John
Cockcroft. Lady Cockcroft related to me
her first impression of Kapitza:

A wild kind of character, untidy, his
overcoat fastened with safety pins,
bursting with energy, his words tum-
bling out ... He drove a high-powered
Lagonda, the sporting car of the day.
Another friendship was with James
Chadwick. Kapitza was best man at
Chadwick’s wedding. He wore his ev-
eryday clothes for the occasion, upgraded
with a borrowed top hat.

Kapitza married Anna Krylova,
daughter of the prominent Soviet math-
ematician, Aleksei N. Krylov. Krylov
and his wife were separated, and Anna
had been living with her mother in Paris
where Kapitza met her while on a holiday.
A warm, sympathetic person, Anna soon
won the heart of Cambridge. J. J.
Thomson, Master of Trinity College at

the time, assigned his daughter Joan the
task of getting to know the wives of the
Fellows of the college, particularly the
younger ones. Joan and Anna became
fast friends. When Joan later married a
Russian named Charnock, the friendship
became a foursome. Joan Charnock
commented on the Kapitzas’ very happy
marriage:

Some women are essentially wives, and
some women are essentially mothers.
Anna was much more a wife than a
mother.

The Kapitzas’ first son v/as christened
in the Russian Orthodox church for the
sake — or under the influence — of Anna’s
mother. Kapitza entreated the priest not
to make the boy an “Anglosax.”

Kapitza, too, made contact easily. He
had long conversations with the poet A. E.
Housman, with whom others had great
difficulty conversing because for extended
periods Housman would say nothing.
People wondered what it was they talked
about. When asked, Kapitza finally re-
plied, “The Church of England.”

Kapitza was also very close to P. A. M.
Dirac. The two spent a great deal of time
in Kapitza’s laboratory, Kapitza teaching
Dirac such arts as how to grind rough
edges off a piece of glass (startling infor-
mation for those who consider Dirac the
ultimate theorist). Together, they wrote
a paper on the reflection of electrons by
standing light waves, an experiment that
could not be performed at the time, hav-
ing to await the laser. Kapitza started a
discussion club, which met Tuesday eve-
nings after dinner, and, while in Cam-
bridge more than thirty years later, I lis-
tened to talks at “The Kapitza Club.”

Kapitza’s experiments

In the laboratory Kapitza worked very
hard and expected others to do likewise.
These “others” included three techni-
cians: an Estonian named Laurmann
who had come with Kapitza from the So-
viet Union; Pearson, the senior techni-
cian, and Frank Sadler, a former ap-
prentice who, at age twenty, was com-
pletely won over at his hiring interview by
Kapitza’s statement, “I’m looking for a
craftsman.” Kapitza warned that the job
was to come before anything else. Sadler
told me:

It was a nice life. I had no ties and
could work all hours. But poor Mrs
Pearson, she never saw her husband.
Kapitza would be in the workshop
saying, “Pearson you cut one, Sadler
another, me the third.” We all mucked
in.

Sadler alsc.recalled evenings when Anna
would come to the laboratory to drag her
husband off to a dinner party he had for-
gotten. As Kapitza was going out the
door, dusting himself off, he would call
back, “I’ll look in afterwards, to see how
you’re doing.”

Sadler confessed he never understood
Kapitza’s many humorous stories, told in

BIOGRAPHY

217

The Institute of Physical Problems built for
Kapitza in the Lenin Hills near Moscow. Part of
Kapitza’s twelve-roomed “cottage” is visible at
the right. Housing for staff is also on the site.

"Kapitzarene” — a language said to be
equidistant from Russian, English and
French. Sadler always knew when to
laugh, however, because Kapitza would
burst into gales of laughter. Sadler was
sure no one else understood the stories
either, except Cockcroft who knew Rus-
sian.

Kapitza carried out pioneer experi-
ments on properties of matter, such as the
electrical resistance of metals, in strong
magnetic fields. As some of the effects
are more pronounced at low tempera-
tures, cryogenic research was added to the
magnetic investigations. Kapitza in-
vented a new and simpler apparatus with
which to liquify helium in quantity at
relatively low cost. His helium liquifier
led to the commercial Collins liquifier.
More laboratory space was needed for his
experiments. The Royal Society pro-
vided funds from a bequest of multimil-
lionaire chemist Ludwig Mond to build a
new laboratory, named after Mond, and
to be directed by Kapitza. At the same
time, Kapitza was appointed Royal Soci-
ety Messel Professor.

The new laboratory was opened in 1933
by Stanley Baldwin, former (and later)
Prime Minister and chancellor of the
university at the time. On the facade, to
the right of the door, was a crocodile. It
had been carved by British sculptor Eric
Gill on commission from Kapitza. There
is considerable commentary on the croc-
odile. In Brighter than a Thousand Suns
by Robert Jungk, Kapitza says, “Mine is
the crocodile of science. The crocodile
cannot turn its head. Like science it must

always go forward with all-devouring
jaws,” although everyone knew the croc-
odile represented Rutherford, except
Rutherford himself. The latter’s
biographer, A. S. Eve, wrote that it was
said the crocodile never turns back and
was accordingly regarded as a symbol of
Rutherford’s scientific acumen and ca-
reer. The crocodile, Eve wrote, is re-
garded in Russia with mingled awe and
admiration. I queried several Russians

on the subject, and one pointed out that
the Russian humor magazine is named
Krokodil. Another, who worked with
Kapitza, said “crocodile is slang for ‘boss’
in Russian.” The London Times, re-
porting the opening of the laboratory said,
“The entrance is guarded by a dragon.”

Kapitza showed Baldwin around, ex-
plained how things worked and pointed
out the special design that ensured the
roof would not blow off in an explosion.

Kapitza addressing a 1956 meeting in Moscow to honor the 250th anniversay of the birth of Ben
Franklin. On such occasions he made indirect appeals for more contact with foreign scientists.

TASS FROM SOVFOTO

218

HISTORY OF PHYSICS

At one point Baldwin asked, “Is that so?”
to which Kapitza replied, “Oh, yes you
can believe me. I’m not a politician.”

Return to the Soviet Union

In the summer of 1934 the Kapitzas
went to the Soviet Union, as they had a
number of previous summers. The first
time had been at the invitation of the
Soviet government. George Gamow
states in his autobiography that, as a
precaution, Rutherford had written the
Soviet Ambassador to Britain for assur-
ance that Kapitza would return to Cam-
bridge in September. The assurance was
granted and Kapitza returned at the
specified time. The same routine was
followed for subsequent visits, except for
1934. Gamow says that Kapitza told
Rutherford the letter of guarantee was not
needed. Cambridge friends say the letter
was slow in coming and Kapitza did not
want to delay his departure. In any case,
Kapitza was certain he would not be de-
tained in the Soviet Union.

When the time came for Kapitza to re-
turn to Cambridge, a telegram arrived
instead. Time passed. When it became
abundantly clear that Kapitza would not
be allowed to return, Anna returned by
herself to seek aid from influential scien-
tists. She devoted months to the effort.

In discussing Kapitza’s detention, one
Englishman told me Rutherford had said
all along, “They’ll getcha.” Dirac said
that incidents and remarks such as the
one Kapitza made to Baldwin may have
kept the English from trying harder to get
him back. “He had trodden on too many
toes,” Dirac said. “He was always impa-
tient with important people who wanted
to see his lab. He wasn’t too polite.”

Once Kapitza had been too busy to
show two visiting Russians around. It is
believed they reported that Kapitza was
doing secret war work, seeing no other
reason for their not having been shown
the laboratory.

Rutherford wrote to Baldwin that So-
viet authorities had commandeered
Kapitza in the belief he would give im-
portant aid to their electrical industry,
and “they have not found out they were
misinformed.” Rutherford also appealed
to the Soviet government for Kapitza’s
return to complete his work “in the in-
terests of science.” The Soviet reply was
eminently reasonable: It was under-
standable that England should want
Kapitza, and the Soviet Union, for its
part, would equally like to have Ruther-
ford. The Soviet Embassy statement
said:

As a result of the extraordinary devel-
opment of the national economy of the
U.S.S.R., the number of scientific
workers available does not suffice and
in these circumstances the Soviet
Government has found it necessary to
utilize for scientific activity within the
country the services of Soviet scientists
who have hitherto been working

The Lomonosov Medal was presented to Kapitza in Moscow, February 1960, to recognize his
achievements in low-temperature physics. Eighteen years later he received the Nobel Prize.

abroad. Kapitza belongs to this cate-
gory.

Kapitza was in a deep depression.
Despite attractive offers, he did not start
work. The story among Russians is that
Kapitza told Premier Molotov, “Don’t
you know a bird in a cage doesn’t sing?”
to which Molotov replied, “This bird will
sing.”

The Kapitza Institute

It was more than a year before the bird
began to sing, and then with not much
voice. When efforts to persuade the So-
viet government to release Kapitza failed,
E. D. Adrian and Dirac were dispatched
to Russia. Adrian’s visit was an official
one; Dirac combined a lecture tour with a
visit to “cheer up” Kapitza, though he
later reported it took Kapitza several
years to come out of his depression. Ad-
rian and Dirac’s mission was followed by
the Soviet purchase of Kapitza’s appara-
tus from the Mond Laboratory for
£ 30 000 — considered a fair price — and

Cockcroft had it packed and shipped.

Meanwhile, Kapitza’s “cage” was being
gilded to his specifications: a replace-
ment for the Mond Laboratory was being
built. Kapitza was given his choice of site
on which to build and the spot he selected,
the best in Moscow according to Nikita
Khruschev’s memoirs, had been desig-
nated for a new American Embassy.
Stalin, however, became disillusioned
with William C. Bullitt, Ambassador to
Moscow from 1933 to 1936, and, infu-
riated by Bullitt’s “hardline” politics,
decreed that Kapitza’s institute and not
the US Embassy would be built on that
choice location.

In addition to the Institute, a “cottage”
consisting of twelve rooms and a terrace
was built for Kapitza. A row of town-
houses for scientific co-workers and
smaller homes for the technical staff were
also constructed. Tennis courts and a
chauffered limousine completed the
package.

The Institute for Physical Problems, as

TASS FROM SOVFOTO

BIOGRAPHY

219

it was called, took two years to build.
Kapitza described the quality of con-
struction as only satisfactory, but in
equipment it was one of the foremost —
not only in the Soviet Union, but in Eu-
rope as well. The bird was chirping, if not
singing. Kapitza said of the precision
lathes, “we can say with pride that the
majority are of Soviet origin.” Every ef-
fort was made to reduce the administra-
tive staff: A simplified bookkeeping
system allowed one accountant to do the
work of five, and nine firemen were re-
duced to a volunteer brigade and an
electric signalling system.

One townhouse occupant was Lev
Landau. Kapitza’s reputation as a mas-
ter string-puller was evidenced in con-
nection with Landau, who, despite his
being Jewish, had been imprisoned in the
1930’s as a German spy. Kapitza
threatened to leave his institute if Landau
were not freed; Landau was freed.

Kapitza went on to criticize relations
between Soviet science and industry,
criticism he kept up through the years.
He argued that Soviet industry, although
sufficiently advanced to make anything
that could be made elsewhere, was geared
to manufacture on a large scale and was
ill-adapted to serve scientific needs of a
smaller scale. The conditions Kapitza
criticized still exist, according to Ameri-
cans who deal with Soviet industry.

In 1941 the Institute was evacuated to
Kazan, capital of the Tatar Republic. No
scientific papers came out of the Institute
between 1941 and 1944, presumably be-
cause it was engaged in war work. The
buildings in Moscow suffered no damage,
and by August 1943 most of the staff was
able to return.

Papers on the superfluidity of liquid
helium published in 1944 represent work
begun before the war. Then, in 1949,
Kapitza published a paper with a some-
what strange title: “On the Problem of
the Formation of Sea Waves by the
Wind.” Similar papers followed: “Dy-
namic Stability of a Pendulum when its
Point of Suspension Vibrates” and “On
the Nature of Ball Lightning” (1955). It
was not until 1959 that Kapitza was again
publishing on subjects that seem appro-
priate, such as the liquefaction of he-
lium.

Kapitza’s friends in the West knew
something was wrong during those post-
war years. In fact, Kapitza was no longer
at the Institute, but working in the garage
of his dacha about twenty miles from
Moscow — under house arrest. He had
been abruptly fired from his position at
the Institute in 1948 and reinstated only
after Stalin’s death.

Khrushchev’s memoirs, published in
1974, fill in some details. In 1939 Kapitza
had built apparatus to produce liquid
oxygen in quantity. Krushchev states:

... as time went by, Stalin began ex-
pressing his displeasure — I’d even say

his indignation — about Kapitza. He

said Kapitza wasn’t doing what he was
supposed to do; . . . the bourgeois press
started howling like 3 pack of mad dogs
about how the Russians must have
gotten their A-bomb from Kapitza be-
cause he was the only physicist capable
of developing the bomb. Stalin was
outraged. He said Kapitza had abso-
lutely nothing to do with the bomb

Kapitza refused to cooperate on the
Soviet bomb project and was accused of
“premeditated sabotage of national de-
fense.” He lost his house, his car and the
other perquisites of the directorship, but
was still a member of the Academy of
Sciences. A small salary from the Acad-
emy enabled him to live in his country
house, but in a more proletarian
manner.

Khrushchev describes his dealings with
Kapitza after Stalin’s death, when Kap-
itza again headed the Institute. Kapitza
tried to impress upon Khrushchev the
importance to the Soviet economy of his
method for producing oxygen. Khrush-
chev had other ideas, stating:

We wanted Kapitza actually to do what
the bourgeois press said he had done:
we wanted him to work on our nuclear
bomb project . . . The point is, he re-
fused to touch any military research.
He even tried to pursuade me that he
couldn’t undertake military work out
of some sort of moral principle.
Khrushchev explains why Kapitza was
not permitted to travel abroad. Khru-
shchev had asked M. A. Lavrentev, an
influential mathematician, about Kapit-
za’s loyalty and was assured that while
Kapitza’s thinking on military subjects
might be “pretty original,” he was still a
loyal citizen. Khrushchev then asked if
Kapitza might know anything about the
military work of others. Lavrentev re-
plied that scientists always talk to one
another about their work, and Khru-
shchev, fearing not Kapitza’s disloyalty
but his talking too much, refused per-
mission for Kapitza to travel abroad.
Behind Khrushchev’s decision was the
desire to conceal Russia’s lack of atomic
weapons from the rest of the world.

Apart from Kapitza’s direct appeals to
travel abroad, he indirectly expressed his
desire in addresses commemorating an-
niversaries of scientists such as Ruther-
ford, Benjamin Franklin, and Lomono-
sov, regarded by Russians as the founder
of their science. After stressing the inter-
national character of science, Kapitza
would point out that Franklin, having
come to science in his forties, was able to
make contributions partly because of his
contact with major scientific figures. Lo-
monosov, on the other hand, is virtually
unknown outside the Soviet Union, his
work not properly credited, owing to his
isolation.

Kapitza’s isolation, however, was not as
extreme as that of Lomonosov. During
the late 1950’s and early 60’s, foreign vis-

itors were allowed and copies of Time,
U.S. News and World Report and Play-
boy could be found in the Institute.
Eventually, Kapitza was even allowed to
travel, but not until in his seventies when
the Soviet Union had become a major
nuclear power.

Visits to the West

Kapitza returned to England in 1966.
It was a sentimental visit. Old friend-
ships were renewed as if there had been no
interruption. There was some debate,
however, as to whether Kapitza’s English
had improved or deteriorated.

Kapitza offered reporters a wry peace
plan involving an exchange of military
scientists. “Then there would be no more
secrets,” he said. He went on to comment
on the “brain drain” of British scientists
to the United States, saying that Russia
was in a more difficult situation, having
no one to drain.

In Cambridge Kapitza stood before the
Mond Laboratory and, gazing at the
crocodile on its facade, put an end to years
of speculation. He admitted that the
crocodile represented Rutherford, saying
“in Russia the crocodile represents the
father of the family.”

Kapitza came to the US for the first
time in 1969 and received an honorary
degree from Columbia University.
Polykarp Kusch, then Vice-President and
Dean of Faculties, called Kapitza’s 1922
paper “On the possibility of an Experi-
mental Determination of the Magnetic
Moment of an Atom” (the last of the six
papers he wrote before going to England)
“clairvoyant.” Kusch himself had been
awarded a Nobel Prize for measuring a
related property.

After the ceremonies came a reception.
I prefaced my questions by telling Ka-
pitza I had already spoken to his wife at
length. “You did well,” he replied. “She is
authorized person.” I questioned him on
his role in the development of the Soviet
H bomb. At that time Sakharov’s name
was unfamiliar and most people thought
Kapitza had directed the project. “I never
did! I never did!” he insisted. “I even suf-
fered for it!”

Back in the Soviet Union, Kapitza no
longer works on low-temperature physics,
having gone to the other extreme — con-
trolled thermonuclear fusion. The work
comes out of his earlier work on ball
lightning, done while under house arrest.
Old physics apparently neither dies nor
fades away.

Old physics won Kapitza his Nobel
Prize last year. The citation was for his
basic inventions and discoveries in the
area of low-temperature physics. (A de-
tailed account of this work was given by
Gloria B. Lubkin in the December 1978
issue of PHYSICS TODAY.) In Stockholm,
after an introduction by the Stockholm
Philharmonic playing Glinka’s overture
to “Ruslan and Ludmilla,” Kapitza ac-
cepted his prize in person. (We were told

220

HISTORY OF PHYSICS

that a large fraction of the award money
went to the purchase of a high-powered
Mercedes. It is not known whether the
manufacturer supplied blueprints.)

The present

Working for the older Kapitza is evi-
dently pretty much the same as working
for the younger Kapitza, as the longevity
of his nickname — “Centaur” — attests.
The name is said to have originated when
someone asked a member of the Institute,
“What sort of man is your boss?” and the
reply was, “It’s difficult to say— half man,
half beast. Maybe we should call him a
centaur.” (The Russian word translated
here as “beast” is used for a domestic la-
boring animal.)

Although he often polarizes people, ev-
eryone agrees Kapitza is cultivated, vital,
witty, and above all, “outspoken.” Over
the years his criticisms have antagonized
people in various high places; he once cri-
ticized Marxist philosophers for their re-

jection of cybernetics which, if followed
by Soviet scientists, would have eliminat-
ed the Soviet Union from the space race.
He later joined intellectuals in appealing
to the Communist Party’s Central Com-
mittee to allow Solzhenitsyn to live and
work without interference. When Zhores
Medvedev suffered detention in a mental
hospital, protests came not only from
Solzhenitsyn and Sakharov as expected,
but from Kapitza as well.

In his eighties, the outspoken Kapitza
now employs the weapon of silence.
When academicians sign a condemnation
of Sakharov for his political utterances,
Kapitza’s silence speaks out eloquently.

Bibliography

This article is based primarily on interviews
with friends and colleagues of Kapitza from
his Cambridge days. Other sources were:

• D. S. Danin, Rutherford, Young Guard
Publishing House of the Central Committee

of the Communist Youth League, Moscow
(1966).

• A. S. Eve, Rutherford, Cambridge University
Press, Cambridge (1939).

• G. Gamow, My World Line: an Informal
Autobiography, Viking, New York (1970).

• R. Jungk, Brighter Than a Thousand Suns:
A Personal History of the Atomic Scien-
tists, (J. Cleugh trans.) Harcourt, Brace,
Jovanovich, New York, (1970).

• N. Khrushchev, Khrushchev Remembers,
the Last Testament, (S. Talbott, ed. and
trans.) Little, Brown (1974).

• P. Kapitza, Peter Kapitsa on Life and
Science, (A. Parry, ed. and trans.) Mac-
millan, New York (1968).

• D. Shoenberg, “Royal Society Mond Labo-
ratory, Cambridge,” Nature 171, 458
(1953).

• P. Kapitza, Collected Papers of P. L. Kap-
itza, (D. Ter Haar, ed. and trans.) Pergamon
Press, London, 1967.

• A. Wood, The Cavendish Laboratory,

Cambridge University Press, Cambridge
(1946). □

BIOGRAPHY

221

The young Oppenheimer:
letters and recollections

Correspondence with friends and colleagues and reminiscences
— his own and others’ — give insights into the development and character
of an important physicist and public figure.

Alice Kimball Smith and Charles Weiner physics today / april i960

A prominent physicist before World
War II, J. Robert Oppenheimer became
the wartime director of the Los Alamos
nuclear weapons laboratory. After the
war he became an influential adviser to
the government on atomic energy, but
fell from favor during the McCarthy
era. This story has become the stuff of
myth and drama. Here we would like
to present glimpses of the less familiar
Oppenheimer — learning, playing, mak-
ing friends, doing physics, winning rec-
ognition— as yet unburdened by the
actuality of the bomb, by fame and by
public responsibilities.

To many of his contemporaries Op-
penheimer was a brilliant scientist, a
dedicated public servant, and a fine
human being in whom virtue far tran-
scended defect and fully compensated
for it. Others saw a man of flawed
judgment, sometimes devious or affect-
ed in personal relations or in public
posture, whose actual contributions did
not match his reputation as a physi-
cist. Oppenheimer is often described
as complex, but complexity is not (in
itself) a trait of personality; it indicates
rather that the observer is puzzled.
What can confidently be said on the
basis of Oppenheimer’s early letters is
that, even when he was a young man,
the world around him, the choices it
offered, and the human beings with
whom he associated were not simple or
easily defined. As Oppenheimer’s per-
sonality became an object of wider
interest, he still maintained an air of
privacy, suggesting an inner self with-
held from public view. People reacted
to this quality with either fascination

Alice Kimball Smith is Dean Emerita of the
Bunting Institute at Radcliffe College and
Charles Weiner is professor of history of
science and technology at the Massachusetts
Institute of Technology. This paper is adapted
from Robert Oppenheimer: Letters and Recol-
lections (Cambridge, MA: Harvard University
Press, 1980).

or displeasure. Throughout his life he
sometimes showed an uncanny ability
to cut through confusion with clarity
and precision. At other times he
groped his way toward answers and
spoke and acted with an ambiguity that
puzzled or antagonized those of a differ-
ent cast of mind.

Yet this man — so difficult to classify,
so selective in his preoccupations and
his friendships, most at home in ab-
struse reaches of mathematical phys-
ics, who never courted approval outside
a small social and intellectual circle,
who was considered unpredictable and
temperamental even by admirers — be-
came the disciplined leader of the pro-
ject which built the atomic bombs
dropped on Japan in August 1945,
thereby revolutionizing warfare and
international relations. Oppenhei-
mer’s subsequent role as weapons ad-
viser and as a leading architect of
American nuclear policy was likewise
an unexpected one.

The correspondence

We have collected many of Oppen-
heimer’s letters from 1922, when he en-
tered Harvard, to 1945, when he resigned
as director of the Los Alamos nuclear
weapons laboratory. The letters help to
explain this man who played no small
part in shaping the events and character
of an era. To supplement the letters we
have drawn upon interviews with Oppen-
heimer and with many of his contempor-
aries. A particularly valuable source is
the interview with Oppenheimer by
Thomas S. Kuhn in November 1963, for
the Archive for History of Quantum
Physics.1

One hundred and sixty seven letters to-
gether with excerpts from the interviews
and other materials were published by
the Harvard University Press in 1980.2
Here we present selections from the
years 1926 to 1939.

Part of Oppenheimer’s attraction, at

first for his friends and later for the
public, was that he did not project the
popularly held image of the scientist as
cold, objective, rational, and therefore
above human frailty, an image that
scientists themselves fostered by un-
derplaying their personal histories and
the disorder that precedes the neat
scientific conclusion. Oppenheimer’s
foibles, his vulnerability, his capacity
for enjoyment and affection are fully
apparent in the early letters. We see a
sensitive, sometimes awkward young
man growing in self-assurance and
finding satisfaction in a widening circle
of friends, especially when personal
compatibility strengthened a bond in
physics.

Later letters shed light on Oppen-
heimer’s role in physics in the 1930’s
when his own interpretation of what he
liked to call style in science was influ-
encing colleagues and students. They
show that certain qualities of Oppen-
heimer the charismatic leader did not
appear overnight — an engaging blend
of hedonism and asceticism, a tough-
minded skepticism tempered at times
by a compassion born of his own strug-
gle into adulthood, and a hardwon ca-
pacity for self-command. Yet the pre-
cocious Harvard student and the
graduate and postdoctoral worker in
Cambridge, Gottingen and Zurich,
making a place for himself in the new
world of quantum physics, was very
much father to the distinguished theo-
retical physicist and the successful
wartime leader. Many of the prewar
letters that we have located deal with
science. Some of these convey Oppen-
heimer’s sense of excitement and a
growing confidence in his ability to
understand and extend the new physics
unfolding all about him; others express
his frustration in attempting to resolve
the difficult problems inherent in the
theory of quantum mechanics. Math-
ematics was the powerful tool that
promised to illuminate the fundamen-

222

HISTORY OF PHYSICS

CERN PHOTO (1962) FROM AIP NIELS BOHR LIBRARY

tal nature of physical reality, and it
was the international language spoken
and written by Oppenheimer and the
other young theorists of his genera-
tion.

Gottingen

After graduating summa cum laude
in chemistry from Harvard in 1925,
Oppenheimer went to Cambridge to
work at the Cavendish Laboratory. His
year there was not happy and his work
on experimental physics was frustrat-
ing; in 1926 he accepted an offer from
Max Born to continue his work in
Gottingen.

To Oppenheimer looking back, this
year represented his “coming into
physics.” As he told Kuhn,1 “When I
got to Cambridge, I was faced with the
problem of looking at a question to
which no one knew the answer but I
wasn’t willing to face it. When I left
Cambridge I didn’t know how to face it
very well but I understood that this was
my job; this was the change that oc-
curred that year. I owe a great deal
just to the existence of the place and
the people who were there; specifically
I owe a great deal to [Ralph H.] Fowler’s
sense and kindness . . . [By the time I
decided to go to Gottingen] I had very
great misgivings about myself on all
fronts, but I clearly was going to do
theoretical physics if I could ... It
didn’t seem to me like foreclosing any-
thing; it just seemed to me like the next
order of business. I felt completely
relieved of the responsibility to go back
into a laboratory. I hadn’t been good, I
hadn’t done anybody any good, and I
hadn’t had any fun whatever; and here
was something I felt just driven to
try.”

The fulfillment of that passionate

urge to contribute to the new physics
helped him to resolve his personal and
professional dilemmas. From that
miserable year in Cambridge Oppen-
heimer emerged a theoretical physicist
as well as his own best therapist.

By 1963 when Oppenheimer remi-
nisced, the tentative nature of the
move to Gottingen had seemingly been
forgotten. At any rate, he did not burn
his bridges when he notified the Board
of Research Studies that he was leaving
Cambridge (letter numbers are from
our book):

Letter 51 to R.E. Priestley

Cambridge, [England]
August 18, 1926

Dear Sir:

I should like to apply to the Board of
Research Studies for permission to
spend two or three terms next year in
Goettingen. My supervisor, Prof. Sir
Joseph Thomson is not at present in
Cambridge. But Prof. Sir Ernest Ruth-
erford has kindly told me that he would

be willing to assure you that my work
here had been satisfactory, and that
the work which I intended to do at
Goettingen was an extension of that
which I have started here. He also
advised me to tell you that I would, at
Goettingen, be under the supervision of
Prof. Dr. Max Born, and that Prof. Born
was particularly interested in the prob-
lems at which I hoped to work. It is
now my intention to return to Cam-
bridge immediately on the conclusion
of my work in Goettingen.

Yours very sincerely,

J.R. Oppenheimer

The year 1926-27 spent at the Univer-
sity of Gottingen was as important to Op-
penheimer’s personal and professional
growth els any comparable period in his
young manhood. He shed the depression
of the previous winter and obtained the
PhD (under Born) and a postdoctoral fel-
lowship for the year to follow. More im-
portant, his standing in the world of
physics was transformed by day-to-day
discussion with major participants in the
development of new theoretical concepts
and by his own contributions to this
work.

Long after the details had faded he
remembered the stimulation of the
Gottingen experience: “In the sense
which had not been true in Cambridge
and certainly not at Harvard, I was
part of a little community of people
who had some common interests and
tastes and many common interests in
physics. I remember this more than I
do lectures or seminars. I think it
quite probable that I attended some of
Born’s lectures, but I don’t remember.

4

I

BIOGRAPHY

223

I’m sure I gave a seminar or two, but I
don’t remember. I met [Richard] Cour-
ant ... I met [Werner] Heisenberg who
came there and I had not met him
before; [I also met Gregor] Wentzel, and
[Wolfgang] Pauli in Hamburg or in
Gottingen so that something which for
me more than most people is important
began to take place; namely I began to
have some conversations. Gradually, I
guess, they gave me some sense and
perhaps more gradually, some taste in
physics, something that I probably
would not have ever gotten to . . . if I’d
been locked up in a room.”1

Oppenheimer’s own surviving corre-
spondence with other physicists during
this period provides only a sporadic
view of his day-to-day efforts to make
physics comprehensible. Individual
letters describe fragments of his work
and these are difficult to understand
and place in perspective today, even by
his students. Some of the ideas he soon
abandoned because they were wrong or
because they did not lead to greater
understanding; others emerged as pub-
lications in the scientific journals.
Even much of the work that survived to
the publication stage is now obsolete.
Like most of the scientific literature
more than a decade old, it has been
superseded by new experimental dis-
coveries and new theoretical formula-
tions. As Robert Serber, one of Op-
penheimer’s students and close col-
laborators, recently reflected, “Things
that are obvious now were not for the
people doing it then. It all falls out
once you know the answer. The prob-
lems they struggled through do not
appear today. But there are other
problems now.”3

A letter to Edwin Kemble, who had
been one of his physics professors at
Harvard, shows how thoroughly Op-
penheimer had become involved in spe-
cific problems then occupying the at-
tention of scientists in Gottingen. This
and subsequent letters to other physi-
cists demonstrate growing familiarity
with the mathematical language of
quantum mechanics and the range of
Oppenheimer’s interest in it. They
also provide vivid glimpses of the infor-
mal communication patterns of scien-
tists as they gossiped and as they pro-
posed solutions to the problems that
concerned them.

that you will surely like it. Even now
there are quite a few American physi-
cists here, and some will be staying on
until the Spring. I expect to be here
until March, & then go back to Cam-
bridge; and I hope that I shall have the
opportunity of seeing you either here or
there.

Almost all of the theorists seems to
be working on ^-mechanics. Professor
Born is publishing a paper on the Adia-
batic Theorem, & Heisenberg on
“Schwankungen [fluctuations].” Per-
haps the most important idea is one of
Pauli’s, who suggests that the usual
Schroedinger ^-functions are only spe-
cial cases, & only in special cases — the
spectroscopic ones — give the physical
information we want. He considers the
(/'-solutions when any set of canonical
variables is chosen as independent. But
of all this you probably know more
than I do. People here are also very
anxious to apply the q-mechanics to
molecules; but so far the only attempt,
Alexandrow’s paper on the H2*-ion,
seems to be completely wrong.

I have been working for some time on
the quantum theory of aperiodic phe-
nomena. It is possible to get the inten-
sity distribution in continuous spectra
on the new theory — and without any
special assumption. And in fact the
theory gives, when applied to a simple
Coulomb model, a very good approxi-
mation to the X-ray absorption law. For
K electrons, for instance, the absorp-
tion per electron is of the form A “z3,
where a lies, except just near the limit,
between 2.5 and 3.1.

Another problem on which Prof.
Born and I are working is the law of
deflection of, say, an a-particle by a
nucleus. We have not made very much
progress with this, but I think we shall
soon have it. Certainly the theory will
not be so simple, when it is done, as the
old one based on corpuscular dyna-
mics.

Please remember me to Professor
Bridgman. And thank you again for
your letter.

J R Oppenheimer

Although at the end of November Op-
penheimer had not yet eliminated the
possibility of returning to the Caven-
dish, the collaboration with Born was
so satisfying and productive that he
soon decided to complete his doctorate
in Gottingen. As indicated in the let-
ter to Kemble, Oppenheimer was con-
tinuing work started in England on the
application of quantum theory to tran-
sitions in the continuous spectrum.
This research was embodied in the
dissertation for which he received the
PhD degree from the University of
Gottingen in the spring of 1927. Mean-
while, he also employed quantum me-
chanics to explain scattering. An im-
portant contribution to theoretical

Oppenheimer in 1 926 or 1 927. (Photo cour-
tesy of Frank Oppenheimer.)

physics was a joint paper with Born on
the quantum theory of molecules. The
“Born-Oppenheimer approximation”
remains in use today.

Born’s favorable view of Oppenhei-
mer is recorded in a letter of February
1927 to S.W. Stratton, president of the
Masschusetts Institute of Technology.
“We have here a number of Ameri-
cans, five of them working with me.
One man is quite excellent, Mr. Op-
penheimer, who studied at Harvard
and in Cambridge-England. The oth-
er men did not surpass the average,
but I hope, that not only Oppenhei-
mer, but also some of the other fellows
will get their doctor’s degree during
the next term.”4

Oppenheimer looked back with
mixed feelings upon aspects of the Got-
tingen experience other than physics:
“Although this society was extremely
rich and warm and helpful to me, it was
parked there in a very miserable Ger-
man mood . . . bitter, sullen, and, I
would say, discontent and angry and
with all those ingredients which were
later to produce a major disaster. And
this I felt very much.”1

When Edwin Kemble visited Gottin-
gen in June he was able to report to his
colleague Theodore Lyman that Har-
vard’s odd duckling was looking more
and more like a swan. “Oppenheimer
is turning out to be even more brilliant
than we thought when we had him at
Harvard. He is turning out new work
very rapidly and is able to hold his own
with any of the galaxy of young math-
ematical physicists here. Unfortu-
nately Born tells me that he has the
same difficulty about expressing him-
self clearly in writing which we ob-
served at Harvard.”5

Berkeley and Cal Tech

After postdoctoral work at Harvard,
the California Institute of Technology,
and several European universities, Op-

Letter 53 to Edwin C. Kemble

Gottingen
Physikalisches Institut
Nov 27. [1926]

Dear Dr Kemble,

Many thanks for your kind letter. As
I shall not see Mr. Fowler for some
time, I have taken the liberty of quot-
ing a paragraph from your letter in a
note I sent him.

This term I am spending at Gottin-
gen. It is a very nice place, and I think

224

HISTORY OF PHYSICS

penheimer accepted, in 1929, a joint
appointment at the University of Cali-
fornia in Berkeley and Cal Tech. At
each school he was regarded as the
authority on the new developments in
quantum theory, and soon became an
influential teacher and leader of a ma-
jor school of theoretical physics. As he
recalled later:

“I think that the whole thing has a
certain simplicity. I found myself en-
tirely in Berkeley and almost entirely
at Caltech as the only one who under-
stood what this was all about, and the
gift which my high school teacher of
English had noted for explaining tech-
nical things came into action. I didn’t
start to make a school; I didn’t start to
look for students. I started really as a
propagator of the theory which I loved,
about which I continued to learn more,
and which was not well understood but
which was very rich. The pattern was
not that of someone who takes on a
course and who teaches students pre-
paring for a variety of careers but of
explaining first to faculty, staff, and
colleagues and then to anyone who
would listen what this was about, what
had been learned, what the unsolved
problems were.”1

Among the faculty at Berkeley at
the time of Oppenheimer’s appoint-
ment was Ernest O. Lawrence, who
was to play a dynamic role in making
the department a center for nuclear-
physics research. He and Oppenhei-
mer became close friends. A letter to
Lawrence captures some of the spirit
of the time. It was written shortly
after an APS meeting in New Orleans
(held simultaneously with an AAAS
meeting), as Oppenheimer and his fa-
ther were travelling to Pasadena. Op-
penheimer’s brother Frank had also
been in New Orleans for the Christ-
mas holidays. (Frank, eight years
younger, was then a sophomore at
Johns Hopkins.)

Letter 79 to Ernest O. Lawrence

Texas

Sunday [3 January 1932]
Dear Ernest,

This is an entirely gratuitous little
note, written only to compensate for
the brevity and sketchiness of our time
together in New Orleans, and to thank
you for certain very generous things to
which in that time I did not do full
justice. My brother was very happy at
last to meet you, sorry only that the
times had been so short. He asked me
to tell you this, to send you his greet-
ings, to tell you too with what eager-
ness he was looking to your visit next
summer. We had a fine holiday togeth-
er; and I think that it settled definitely
F rank’s vocation for physics. Seeing so
together a good number of physicists, it
is impossible not to conceive for them a
great liking and respect, and for their
work a great attraction. We went
Thursday with [George] Uhlenbeck and
[L.H.] Thomas to a joint session of
biochemistry and psychology, it was
enormously rowdy and very funny; and
it discouraged an excessive faith in
either of these sciences . . .

I hope that in this week before term
you will be able to get a good deal of
work done. I suppose that it is too much
to hope that by the beginning of term
the big magnet [for the cyclotron that
Lawrence was building] will be ready;
but perhaps by then your contractors
will be done. If there are any minor
theoretical problems to which you need
urgently the answer, tell them to [J.
Franklin] Carlson or [Leo] Nedelsky;
and if they are stumped let me have a
try at them. When you see [David H.]
Sloan please give him my wishes for a
good recovery; and to Berkeley my
greetings.

Thank you again for your fine Christ-
mas present. Let things go well with
you. a bientot

Robert

Berkeley, mid-1930’s. Oppenheimer with
Enrico Fermi and Ernest O. Lawrence. (Cour-
tesy of AIP Niels Bohr Library: Fermi Film.)

In his interview with Kuhn, Oppen-
heimer discussed a change he under-
went during these years:

“I would think that the transition
was . . . from that of a person who had
been learning and also explaining in
European centers and in Harvard and
Cqltech to someone who couldn’t much
any longer learn from masters but
could learn from the literature and
from what he did himself, and who had
a lot of explaining to do because there
was no one else. I think it was not such
a sudden transition. Living a life in
which you lecture three hours a week
and have a seminar [or] another lecture
two hours a week leaves you a lot of
time for physics and for lots of other
things and I wasn’t an altered charac-
ter. I was still primarily a student in
terms of what I spent time on . . .

[Lecturing] took energy, a great deal
of energy, but I didn’t have to look
much up in the book and it was more a
question of keeping the presentation
fresh and making it sharper and
richer. I would think that the big
change was that I wasn’t an apprentice
any longer and I had decided where to
make my bed ... In a certain sense I
had not grown up but had grown up a
little, and I think if circumstances had
been such that I had had to teach to
make a living earlier it probably would
have been better for me. I don’t think
it would have derailed my interest in
physics but I think it would perhaps
first of all have made it necessary for
me to learn what I wanted to know.”1

Brotherly advice

Oppenheimer wrote many long let-
ters to his brother, reporting on his own
life, offering advice and sharing ideas
with him. They spent happy summers
together at the Oppenheimer family’s
ranch, which the brothers named Perro
Caliente, in the upper Pecos Valley,
New Mexico, near Santa Fe. Frank
studied at Johns Hopkins, graduating
(after three years) in 1933. Following
Robert’s advice, Frank started with
biology, but found himself seduced by
physics.

Letter number 83 to Frank Oppenheimer

Berkeley
Sunday [ca. fall 1932]

Dear Frank,

There has never been so long a time
which I have let pass without a letter;
and never a time when so constantly I
have enjoyed your company. Our com-
mon life last summer left in me a fine
deposit which I have been tapping all
these months, a great repository of

-

BIOGRAPHY

225

your words and gestures and of the
good hours which we shared. Even
now, perhaps, with an answer to your
marvellous letters so long overdue, I
should not be writing to you if I had not
the hope and project of another com-
mon holiday in mind. And that is
Christmas . . . My suggestion for a half
way meeting is perhaps foolish: but
how would New Mexico do, that we
have neither of us seen in winter, that
would be friendly and not quite so far
for you as this coast? The only certain
point for me is that we should be
together, and that we should make the
time as pleasant and as right for father
as we can.

Your courses sound swell; only I am
distressed by this, that they are cover-
ing an area very much like the one I
cover in my introduction to theoretical
physics; for I have an arrogant and
stubborn wish that you might be learn-
ing these beautiful things from me. I
feel sure that your three courses would
profit by union: that the reciprocal
illumination which function theory,
vector analysis, and potential theory
give each other is indispensable to a
profound understanding of any one of
them. Maybe you can try to fill in the
bridges for yourself; and I shall try to
get you a set of notes for next summer
that will help to anchor them. You
know of course that I have pretty mixed
feelings about this program of yours in
which theoretical physics plays such a
large part: it is the most delightful and
rewarding study in the world, and I can
be only glad that you are enjoying it,
glad too that we shall always be able to
share this treasure. It is only the
implications of the course that trouble
me: the possibility that you are more
and more deeply committing yourself
to a vocation which you will regret; the
possibility that your motives in this
choice — and I wish that I might dismiss
this, but only you can — are not wholly
in physics and your liking for it. I take
it that the biology at Hopkins is abomi-
nable— this from many sources: and
that the only other academic study of
any consequence, that of hard lan-
guages, leaves you pretty cold; that
does not leave much but vectors and
Cauchy’s theorem for you to try. But
let me urge you with every earnestness
to keep an open mind: to cultivate a
disinterested and catholic interest in
every intellectual discipline, and in the
non academic excellences of the world,
so that you may not lose that freshness
of mind from which alone the life of the
mind derives, and that your choice,
whatever it be, of work to do, may be a
real choice, and one reasonably free.
Just yesterday I was over in Marin, the
country on the northern seaward arm
of San Francisco bay; it was a grey day,
with heavy fog blowing in from the sea;
and the little lighthouses at all the

perilous points cut off from. ..the world by
the mountains behind and the fog banks
out to sea. I suppose that only very gifted
and industrious lighthouse keepers get to
live in such places; but their mere exis-
tence makes me wonder how any man of
sense can ever adopt any other voca-
tion... .

The work is fine: not fine in the
fruits but the doing. There are lots of
eager students, and we are busy study-
ing nuclei and neutrons and disintegra-
tions; trying to make some peace be-
tween the inadequate theory and the
absurd revolutionary experiments.
Lawrence’s things are going very well;
he has been disintegrating all manner
of nuclei, apparently with anything at
all that has an energy of a million
volts. We have been running a nuclear
seminar, in addition to the usual ones,
trying to make some order out of the
great chaos, not getting very far with
that. We are supplementing the paper
I wrote last summer with a study of
radiation in electron electron impacts,
and worrying about the neutron and
Anderson’s positively charged elec-
trons, and cleaning up a few residual
problems in atomic physics. I take it
that there will be a lull in the theory for
a time; and that when the theory ad-
vances, it will be very wild and very
wonderful indeed. - — I am reading the
Cakuntala with Ryder; and at our next
meeting shall afflict you with clumsy
translations of the superb poems . . .

Write to me pretty soon, if only to tell
me what plans for the holidays you like
best. God keep you; and let the days be
rich and sweet.

Robert

Oppenheimer’s remark about "trying

to make some peace between the inad-
equate theory and the absurd revolu-
tionary experiments” should be viewed
against a background of important
achievements in 1932 that focused the
attention of the physics community on
nuclear and cosmic ray research. In
January Harold C. Urey at Columbia
University discovered a heavy isotope of
hydrogen (deuterium). In February
James Chadwick at the Cavendish Lab-
oratory demonstrated the existence of
the neutron, a new nuclear particle. In
April John Cockcroft and E.T.S. Wal-
ton, also of the Cavendish, disintegrated
the nuclei of light elements by bombard-
ing them with artificially accelerated
protons. In August, at Caltech, Carl D.
Anderson’s photographs of cosmic ray
tracks showed the existence of the posi-
tron, the positively charged electron.
Soon after, at Berkeley, Ernest Law-
rence and his students Stanley Living-
ston and Milton White used their new
particle accelerator, the cyclotron, to
disintegrate nuclei. These discoveries
and techniques provided theorists with
exciting challenges and opportunities.2

After Johns Hopkins, Frank followed
Robert’s footsteps and continued his
studies at the Cavendish, where he
worked on problems related to nuclear
physics, a subject of mutual interest.
Robert wrote him about these and oth-
er problems.

Letter 93 to Frank Oppenheimer

Pasadena
June 4 [1934]

Dear Frank,

Only a very long letter can make up
for my great silence, and for the many
sweet things for which I have to thank
you, letters and benevolences stretch-

Oppenheimer and Lawrence on a visit to
the Oppenheimer family’s ranch, Perro Ca-~
liente, near Cowles, New Mexico, before
1932. (Courtesy of Molly B. Lawrence.)

J

226

HISTORY OF PHYSICS

ing now over many months . . .

Have you seen what Gamow has done
about angular momentum quantum
numbers for the levels of the radioac-
tive series? It will be wrong in detail
but right in principle. My own labors
have been largely devoted to disentan-
gling the still existing miseries of posi-
tron theory; and Furry and I have just
published another manifesto after
which I hope to be able to forget the
subject for a time. All of us have been
working quite hard, and if you were
here I should have a good many minor
things of which to tell you; but only in
conversation could I do sufficiently ca-
sual justice to them. As you undoubt-
edly know, theoretical physics — what
with the haunting ghosts of neutrinos,
the Copenhagen conviction, against all
evidence, that cosmic rays are protons,
Born’s absolutely unquantizable field
theory, the divergence difficulties with
the positron, and the utter impossibil-
ity of making a rigorous calculation of

anything at all — is in a hell of a way.

In a fortnight I shall be driving to
Ann Arbor, to have three weeks there,
exposing positrons. Gamow will be
there, and Uhlenbeck, and it should be
pleasant. They asked me next year to
go to Princeton, where Dirac will be,
and permanently to Harvard. But I
turned down these seductions, thinking
more highly of my present jobs, where
it is a little less difficult for me to
believe in my usefulness, and where the
good California wine consoles for the
hardness of physics and the poor pow-
ers of the human mind.

[Robert]

Nuclear fission

Glenn T. Seaborg, then an instructor
in chemistry, later described the re-
sponse at Berkeley to the discovery of
nuclear fission: “I remember ... a
seminar in January 1939 when new
results ... on the splitting of uranium
with neutrons were excitedly discussed;

I do not recall ever seeing Oppenhei-
mer so stimulated and so full of ideas.”6

News of research on nuclear fission
and interest in the enormous amounts
of energy that might be released were
the focus of a letter to his good friend
George Uhlenbeck.

At the same time, Oppenheimer was
working on the application of general
relativity and nuclear physics to theo-
retical astrophysics. The significance
of his work on neutron stars and gravi-
tational contraction became evident in
the 1960’s and 1970’s when the reality
of neutron stars, pulsars, and black
holes was established through new as-
tronomical research techniques. This
work and his continuing interest in the
radioactivity of the “mesotron” (the
muon) is also mentioned in the letter.

Letter 106 to George Uhlenbeck

Berkeley
Feb. 5 [1939]

Dear George,

I want to answer your fine long very
welcome letter at once, partly to show
how happy I was to have it . . .

Here too there is further evidence for
the bursting U. They have recorded
the heavy tracks in a differential cham-
ber, and seen them, very prominent

Dinner at the International House at Berke-
ley, around 1939. With Oppenheimer are
Chien-Shiung Wu and Emilio Segrd. (Courtesy
of Emilio Segrp; AIP Niels Bohr Library.)
A sailing expedition on the ZOrichsee, circa
1930: Oppenheimer, l.l. Rabi, H.M. Mott-
Smith and Wolfgang Pauli. (Photo by Rudolph
Peierls. Courtesy of AIP Niels Bohr Library.)

BIOGRAPHY

227

Los Alamos and after

“I think that the world in which we shall
live these next 30 years will be a pretty
restless and tormented place; I do not
think that there will be much of a compro-
mise possible between being of it, and
being not of it.”

Robert Oppenheimer
to Frank Oppenheimer, 1 0 August 1 93 1

After the start of World War II, Robert
Oppenheimer was very much of the
world. In 1942 he became coordinator of
all fast-neutron research in the US project
to develop an atomic bomb. During 1942
and 1943 much of the work on nuclear
weapons was centralized, becoming the
Manhattan project, and a laboratory was
established at Los Alamos, with Oppenhei-
mer as its scientific director.

After the war, Oppenheimer accepted an
offer to become director of the Institute for
Advanced Study in Princeton. He contin-
ued his government service, giving advice
on atomic energy, and became chairman
of the General Advisory Committee to the
Atomic Energy Commission. His ability to
give succinct summaries of long discus-
sions and clear statements of complex
technical issues made him a valuable
member of many advisory panels.

By the 1 950’s he was a highly respected
figure, admired for his unique wartime
contribution and for his unstinting service

to his country in time of peace. In the
meantime, however, the political climate in
the US had changed, and in 1954 the AEC
suspended Oppenheimer’s security clear-
ance and convened a special board to
determine the validity of charges that his
left-wing activities and associations in the
late 1 930’s — which he had put aside as the
war started — made it unwise to trust him
with classified information. A further
charge involved his postwar work: When
the AEC rejected the General Advisory
Committee’s unanimous recommendation
against a crash program to develop a
hydrogen bomb, Oppenheimer’s lack of
enthusiasm for the project was said to
have deterred some scientists from work-
ing on it.

After lengthy hearings, the panel and the
AEC voted to revoke Oppenheimer’s secu-
rity clearance. Many of the politicians and
scientists who had frequently sought Op-
penheimer’s views had been replaced by
others, who sought advice more consistent
with their own values and priorities, and the
votes reflect that shift in power. Attempts
to discredit Oppenheimer, however, were
vigorously denounced and never fully
succeeded.

The hearings caused Oppenheimer a
great deal of anguish, but he survived the
ordeal surprisingly well. Although one
could have expected him to have felt

defeated or disgraced, he maintained his
dignity after the AEC verdict and showed
no rancor or bitterness in his public state-
ments. In 1963 he received the AEC’s
Enrico Fermi Award for outstanding contri-
butions to atomic energy. In accepting the
award from President Johnson he said “I
think it is just possible, Mr. President, that it
has taken some charity and some courage
for you to make this award today. That
would seem to be a good augury for all our
futures.”

After the war, he continued to work on
theoretical physics, although his productiv-
ity, as measured by papers published, was
much less than earlier. But he “was
always there to stimulate, to discuss, to
listen to ideas.”8 For physicists he became
a catalyst and critic, organizing confer-
ences, encouraging younger scientists and
new ideas (although he was also often
intolerant of views that differed from his).

For the general public he became an
interpreter of the atomic age and a spokes-
man for the cultural values of science.

He retired from the Institute in 1966,
when a malignant throat tumor required
surgery, but he maintained, as much as
possible, his connections with his friends
and colleagues and his commitments to
organizations. On 18 February 1967,
Robert Oppenheimer, 62 years old, died at
his home in Princeton. — T. von Foerster

over the haze of recoil protons and the
faint alpha tracks, from a U foil bom-
barded by neutrons in a very low pres-
sure cloud chamber. Also Abelson
showed that the 72 hour period follows
chemically Te, and emits an X ray
which by differential critical absorp-
tion can be positively identified as the
K alpha, and a little K beta, of Iodine.
The next activity after Te separates out
with I chemically. We too of course
have been thinking of the 1018 ergs per
gram. It seems to me that the pieces
after parturition must be highly ex-
cited, if only because of their anoma-
lous charge distribution. Some of that
must go into radiation, but one would
expect neutrons too. So I think it
really not too improbable that a ten cm
cube of uranium deuteride (one should
have something to slow the neutrons
without capturing them) might very
well blow itself to hell.

There would be much physics to tell,
in exchange for your good account,
perhaps too much for a letter . . . We
have been working here too on static
and nonstatic solutions for very heavy
masses that have exhausted their nu-
clear energy sources: old stars perhaps
which collapse to neutron cores. The
results have been very odd, will be in
part out so soon that I won’t bother to
write them here — I have gradually
talked myself into believing the meso-
tron decay, although the evidence is not
much better than it was two years ago

when we first were thinking of it. The
Pasadena people promise to do a really
clean experiment with ionization
chambers in lakes 4000 m apart next
summer.

Two more points, and I shall write
soon again. For the first, we have been
hoping to get to Perro Caliente quite
early in June this year. It is a very
beautiful month there, without rain,
but with snow in the peaks and very
green. How is it: could you and Else
come? Don’t forget: not the time nor
the place nor your welcome . . .

Say a warm greeting from me to Else,
whose generosity reopened this long
dormant correspondence; tell her to
take good care of herself so she can ride
a horse next June.

hasta luegito

Robert

(Philip H. Abelson, a doctoral candi-
date at Berkeley, was an assistant in
the Radiation Lab. When the news of
fission reached Berkeley, Abelson im-
mediately saw that the research he was
doing for his dissertation might have
led to the discovery. As he later re-
called,7 “I almost went numb as I real-
ized that I had come close but had
missed a great discovery.”)

Oppenheimer’s involvement in re-
search on nuclear fission was, at first,
only incidental and theoretical. Only
in 1941 did he get involved in the
wartime effort, starting as director of

fast-neutron research in Berkeley. In
the course of 1943 the Los Alamos lab
was established, with Oppenheimer as
its director, in the hills overlooking
Santa Fe, near the country where he
had earlier spent such happy vaca-
tions. That appointment marks the
end of the private Oppenheimer.

References

1. Interview with J. Robert Oppenheimer
by Thomas S. Kuhn, 18 November 1963,
Archive for History of Quantum Physics,
AIP Niels Bohr Library, and other
repositories.

2. Robert Oppenheimer: Letters and Recollec-
tions, Alice Kimball Smith, Charles Weiner,
eds., Harvard U.P., Cambridge Mass. (1980),
pap. ed. 1981.

3. Interview with Robert Serber by Charles
Weiner, 25 May 1978, AIP Niels Bohr
Library.

4. Born to Stratton, 13 February 1927, Insti-
tute Archives and Special Collections;
MIT Libraries. Quoted in K. Sopka,
“Quantum Physics in America,” PhD
thesis, Harvard, 1976.

5. Kemble to Lyman, 9 June 1929, Harvard
University Archives. Quoted in K.
Sopka, ref. 4.

6. G.T. Seaborg, in I I. Rabi et. al., Oppenhei-
mer, Scribner’s, New York (1969), page
48.

7. P.H. Abelson, in All in Our Time: The
Reminiscences of Twelve Nuclear Pio-
neers, J. Wilson, ed., Bulletin of the Atom-
ic Scientists, Chicago (1975), page 28.

8. H. Bethe, Science 155, 1081 (1967). □

228

HISTORY OF PHYSICS

Robert G. Sachs

When in 1963 she received the Nobel
Prize in Physics, Maria Goeppert
Mayer was the second woman in his-
tory to win that prize — the first being
Marie Curie, who had received it sixty
years earlier — and she was the third
woman in history to receive the Nobel
Prize in a science category. This ac-
complishment had its beginnings in her
early exposure to an intense atmos-
phere of science, both at home and in
the surrounding university communi-
ty, a community that provided her with
the opportunity to follow her inclina-
tions and to develop her remarkable
talents under the guidance of the great
teachers and scholars of mathematics
and physics. Throughout her full and
gracious life, her science continued to
be the theme about which her activities
were centered, and it culminated in her
major contribution to the understand-
ing of the structure of the atomic nu-
cleus, the spin-orbit-coupling shell
model of nuclei.

Gottingen

Maria Goeppert was born on 28 June
1906 in Kattowitz (now Katowice), Up-
per Silesia (then in Germany), the only
child of Friedrich Goeppert and his
wife, Maria, nee Wolff. In 1910 the
family moved to Gottingen, where Frie-
drich Goeppert became Professor of
Pediatrics. Maria spent most of her life
there until her marriage.

On 19 January 1930 she married
Joseph E. Mayer, a chemist, and they
had two children: Maria Ann, now
Maria Mayer Wentzel, and Peter Con-
rad. Maria Goeppert Mayer became a
citizen of the United States in 1933.
She died on 20 February 1972.

Both her father’s academic status
and his location (Gottingen) had a pro-
found influence on her life and career.
She was especially proud of being the
seventh straight generation of univer-
sity professors on her father’s side. Her
father’s personal influence on her was
great. She is quoted as having said that
her father was more interesting than
her mother: “He was after all a scien-
tist.”1 She was said to have been told
by her father that she should not grow

Robert G. Sachs is professor in the Enrico
Fermi Institute and the physics department of
the University of Chicago. He was Maria
Mayer’s first graduate student and was direc-
tor of the theoretical physics division of Ar-
gonne National Laboratory in 1946 when
Mayer received an appointment to the lab.

Maria Geeppert Mayer
— two fold pioneer

PHYSICS TODAY / FEBRUARY 1982

Although Maria Mayer made significant contributions
(leading to the Nobel Prize) starting in 1930, it was 30
years before she received a full-time faculty appointment.

BIOGRAPHY

229

up to be a woman, meaning a house-
wife, and therefore decided, “I wasn’t
going to be just a woman.”2

The move to Gottingen came to domi-
nate the whole structure of her educa-
tion, as might be expected. Georgia
Augusta University, better known sim-
ply as “Gottingen,” was at the height of
its prestige, especially in the fields of
mathematics and physics, during the
period when she was growing up. She
was surrounded by the great names of
mathematics and physics. David Hil-
bert was an immediate neighbor and
friend of the family. Max Born came to
Gottingen in 1921 and James Franck
followed soon after; both were close
friends of the Goeppert family. Ri-
chard Courant, Hermann Weyl, Gustav
Herglotz, and Edmund Landau were
professors of mathematics.

The presence of these giants of math-
ematics and physics naturally attract-
ed the most promising young scholars
to the institution. Through the years,
Maria Goeppert came to meet and
know Arthur Holly Compton, Max
Delbrueck, Paul A. M. Dirac, Enrico
Fermi, Werner Heisenberg, John von
Neumann, J. Robert Oppenheimer,
Wolfgang Pauli, Linus Pauling, Leo
Szilard, Edward Teller and Victor
Weisskopf. It was the opportunity to
work with James Franck that led to
Joseph Mayer’s coming to Gottingen
and gave him the chance to meet and
marry her.

Maria Goeppert was attracted to
mathematics very early and planned to
prepare for the university, but there
was no public institution in Gottingen
serving to prepare girls for this pur-
pose. Therefore, in 1921 she left the
public elementary school to enter the
Frauenstudium, a small private school
run by sufragettes to prepare those few
girls who wanted to seek admission to
the university for the required exami-
nation. The school closed its doors
before the full three-year program was
completed, but she decided to take the
university entrance examination
promptly in spite of her truncated for-
mal preparation. She passed the ex-
amination and was admitted to the
university in the spring of 1924 els a
student of mathematics. Except for
one term spent at Cambridge Univer-
sity in England, her entire career as a
university student was completed at
Gottingen.

In 1924 she was invited by Max Born
to join his physics seminar, with the
result that her interests started to shift
from mathematics to physics. It was

just at this time that the great develop-
ments in quantum mechanics were tak-
ing place, with Gottingen els one of the
principal centers; in fact, Gottingen
might have been described as a “caul-
dron of quantum mechanics” at that
time, and in that environment Maria
Goeppert was molded as a physicist.

As a student of Max Born, a theoreti-
cal physicist with a strong foundation
in mathematics, she wels well trained in
the mathematical concepts required to
understand quantum mechanics. This
and her mathematics education gave
her early research a strong mathemat-
ical flavor. Yet the influence of James
Franck’s nomathematical approach to
physics certainly became apparent lat-
er. In fact, a reading of her thesis
reveals that Franck already had an
influence at that stage of her work.

She completed her thesis and re-
ceived her doctorate in 1930. The the-
sis was devoted to the theoretical treat-
ment of double-photon processes. It
was described many years later by
Eugene Wigner as a “masterpiece of
clarity and concreteness.” Although at
the time it was written the possiblity of
comparing its theoretical results with
those of an experiment seemed remote,
if not impossible, double-photon phe-
nomena became a matter of consider-
able experimental interest many years
later, both in nuclear physics and in
astrophysics. Now, as the result of the
development of lasers and nonlinear
optics, these phenomena are of even
greater experimental interest.

Johns Hopkins

After receiving her degree, she mar-
ried and moved to Baltimore, where
her husband, Joseph Mayer, took up an
appointment in the chemistry depart-
ment of Johns Hopkins University.
Opportunities for her to obtain a nor-
mal professional appointment at that
time, which was at the height of the
Depression, were extremely limited.
Nepotism rules were particularly strin-
gent then and prevented her from be-
ing considered for a regular appoint-
ment at Johns Hopkins; nevertheless,
members of the physics department
were able to arrange for a very modest
assistantship, which gave her access to
the university facilities, provided her
with a place to work in the physics
building, and encouraged her to partici-
pate in the scientific activities of the
university. In the later years of this
appointment, she also had the opportu-
nity to present some lecture courses for
graduate students.

At the time, the attitude in the phy-
sics department toward theoretical
physics gave it little weight as com-
pared to experimental research; how-
ever, the department included one out-
standing theorist, Karl Herzfeld, who
carried the burden of teaching all of the
theoretical graduate courses. Herzfeld
was an expert in classical theory, espe-
cially kinetic theory and thermody-
namics, and he had a particular inter-
est in what hsis come to be known as
chemical physics. This was also Joseph
Mayer’s primary field of interest, and
under his and Herzfeld’s guidance and
influence Maria Mayer became active-
ly involved in this field, thereby deep-
ening and broadening her knowledge of
physics.

However, she did not limit herself to
this one field but took advantage of the
various talents existing in the Johns
Hopkins department, even going so far as
to spend a brief period working with R.
W. Wood, the dean of the Johns Hopkins
experimentalists. Another member of
the department with whom she had a
substantial common interest was Ger-
hard Dieke. The Mathematics Depart-
ment, which was quite active at that
time, included Francis Murnaghan and
Aurel Wintner, with whom she devel-
oped particularly close connections.
However, the two members of the Johns
Hopkins faculty who had the greatest in-
fluence were her husband and Herzfeld.
N ot only did she write a number of papers
with Herzfeld in her early years there,
but also they became close, lifelong
friends.

The rapid development of quantum
mechanics was having a profound ef-
fect in the field of chemical physics in
which she had become involved, and
the resulting richness and breadth of
theoretical chemical physics was so
great as to appear to have no bounds.
She was in a particularly good position
to take advantage of this situation,
since no one at Johns Hopkins had a
background in quantum mechanics
comparable to hers. In particular, she
became involved in pioneering work on
the structure of organic compounds
with a student of Herzfeld’s, Alfred
Sklar; and in that work she applied her
special mathematical background, us-
ing the methods of group theory and
matrix mechanics.

During the early years in Baltimore,
she spent the summers of 1931, 1932
and 1933 back in Gottingen, where she
worked with her former teacher, Max
Born. In the first of those summers she
completed with him their article in the

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230

HISTORY OF PHYSICS

Handbuch der Physik, “Dynamische
Gittertheorie der Kristalle.” In 1935
she published her important paper on
double beta-decay, representing a di-
rect application of techniques she had
used for her thesis, but in an entirely
different context.

Later, James Franck joined the fa-
culty at Johns Hopkins and renewed
his close personal relationship with the
Mayers. Also in that later period, Ed-
ward Teller became a member of the
faculty of George Washington Univer-
sity, in nearby Washington, D. C., and
she looked to him for guidance in the
developing frontiers of theoretical phy-
sics. At about the same time, she be-
came deeply involved in a collaboration
with Joseph Mayer in writing the book
Statistical Mechanics, published in
1940.

When, as her first bona fide student,
I turned to her for guidance in choosing
a research problem, nuclear physics
was on the rise; she told me that it was
the only field worth considering for a
beginning theorist. She took me to
Teller to ask his advice about possible
research problems. Our resulting joint
work was her first publication in the
field of nuclear physics. My thesis
problem on nuclear magnetic moments
was also selected with Teller’s help,
and she gave her guidance throughout
that work, suggesting application to
this problem in nuclear physics of tech-
niques of quantum mechanics in which
she was so proficient. These two forays
into the field were her only activities in

the physics of nuclear structure until
after World War II.

Her approach to quantum mechan-
ics, having been so greatly influenced
by Born, gave preference to matrix
mechanics over Schrodinger’s wave
mechanics. She was very quick with
matrix manipulations and in the use of
symmetry arguments to obtain
answers to a specific problem; this abi-
lity stood her in good stead in her later
work on nuclear shell structure, which
led to her Nobel Prize. She appeared to
think of physical theories, in general,
and quantum mechanics, in particular,
as tools for solving physics problems
and was not much concerned with the
philosophical aspects or the structure
of the theory.

When she had the opportunity to
teach graduate courses, her lectures
were well organized, very technical,
and highly condensed. She spent little
time on background matters of physical
interpretation. Her facility with the
methods of theoretical physics was
overwhelming to most of the graduate
sutdents, in whom she inspired a con-
siderable amount of awe. At the same
time, the students took a rather roman-
tic view of this young scientific couple,
known as “Joe and Maria,” and felt
that it was a great loss when they left
Johns Hopkins to go to Columbia Uni-
versity in 1939.

Columbia

At Columbia University, where Jo-
seph Mayer had been appointed to an

associate professorship in chemistry,
Maria Mayer’s position at first was
even more tenuous than at Johns Hop-
kins. The chairman of the physics
department, George Pegram, arranged
for an office for her, but she had no
appointment.

This was the beginning of a close
relationship between the Mayers and
Harold Urey and his family, a relation-
ship which was to continue throughout
her life, as they always seemed to turn
up in the same places in later years.
Willard Libby became a good friend,
and it was at Columbia that she first
began to come under the influence of
Enrico Fermi, although she had al-
ready met him in her first summer in
the United States (1930) at the Univer-
sity of Michigan Special Summer Ses-
sion in Physics. The Mayers also saw
much of 1. 1. Rabi and Jerrold Zacharias
during their years at Columbia.

She quickly put to work her talent
for problem solving when Fermi sug-
gested that she attempt to predict the
valence-shell structure of the yet-to-be-
discovered transuranium elements. By
making use of the very simple Fermi-
Thomas model of the electronic struc-
ture of the atom, she came to the
conclusion that these elements would
form a new chemical rare-earth series.
In spite of the oversimplifications of the
particular model, this subsequently
turned out to be a remarkably accurate
prediction of their qualitative chemical
behavior.

In December 1941, she was offered
her first real position: a half-time job
teaching science at Sarah Lawrence
College; she organized and presented a
unified science course, which she devel-
oped as she went along during that first
presentation. She continued, on an
occasional basis, to teach part-time at
Sarah Lawrence throughout the war.

She was offered a second job opportu-
nity in the spring of 1942 by Harold
Urey, who was building up a research
group devoted to separating U-235
from natural uranium as part of the
work toward the atomic bomb. This
ultimately became known as Columbia
University’s Substitute Alloy Materi-
als (SAM) Project. She accepted this
second half-time job, which gave her an
opportunity to use her knowledge of
chemical physics. Her work included
research on the thermodynamic pro-
perties of uranium hexafluoride and on
the theory of separating isotopes by
photochemical reactions, a process
that, however, did not develop into a
practical possibility at that time.
(Much later, the invention of the laser
reopened that possibility.)

Edward Teller arranged for her to
participate in a program at Columbia
referred to as the Opacity Project,
which concerned the properties of mat-
ter and radiation at extremely high

Goeppert-Mayer and
husband, Joseph
Mayer, were married in
1 930; Maria was 24 and
Joseph was 26. Mayer
is emeritus professor of
chemistry at the Univer-
sity of California, San
Diego.

BIOGRAPHY

231

temperatures and had a bearing on the
development of the thermonuclear
weapon. Later, in the spring of 1945,
she was invited to spend some months
at Los Alamos, where she had the
opportunity to work closely with Teller,
whom she considered to be one of the
world’s most stimulating collaborators.

Chicago

In February of 1946, the Mayers
moved to Chicago where Joe had been
appointed professor in both the chemis-
try department and the newly formed
Institute for Nuclear Studies of the

Goeppert-Mayer and
colleagues — with Max
Born (left); with hus-
band and Karl Herzfeld
(at right above) and
(right) Robert Atkinson
(extreme left) and En-
rico Fermi (center).

University of Chicago. At the time, the
university’s nepotism rules did not per-
mit the hiring of both husband and wife
in faculty positions, but Maria became
a voluntary associate professor of phy-
sics in the institute, a position which
gave her the opportunity to participate
fully in activities at the university.

Teller had also accepted an appoint-
ment at the University of Chicago, and
he moved the Opacity Project there,
giving Maria Mayer the opportunity to
continue with this work. It was accom-
modated in the postwar residuum of
the Metallurgical Laboratory of the
university where, in its heyday during
the war, the initial work on the nuclear
chain reaction had been carried out.
She was hired as a consultant to the
Metallurgical Laboratory so that she
could continue her participation in this
project, and several students from Co-
lumbia who had become graduate stu-
dents at Chicago worked under her
guidance.

The Metallurgical Laboratory went
out of existence to make way for estab-
lishing Argonne National Laboratory
on 1 July 1946, under the aegis of the
newly formed Atomic Energy Commis-
sion. She was offered and was pleased

to accept a regular appointment as
senior physicist (half-time) in the theo-
retical physics division of the newly
formed laboratory. The main interest
at Argonne was nuclear physics, a field
in which she had had little experience,
and so she gladly accepted the opportu-
nity to learn what she could about the
subject. She continued to hold this
part-time appointment throughout her
years in Chicago, while maintaining
her voluntary appointment at the uni-
versity. The Argonne appointment
was the source of financial support for
her work during this very productive
period of her life, a period in which she
made her major contribution to the
field of nuclear physics, the nuclear
shell model, which earned her the No-
bel Prize.

Since the mission of Argonne Nation-
al Laboratory at the time was, in addi-
tion to reseach in basic science, the
development of peaceful uses of nu-
clear power, she also became involved
in applied work there. She was the
first person to undertake the solution
by electronic computer of the criticality
problem for a liquid metal breeder
reactor. She programmed this calcula-
tion (using the Monte Carlo method) for

eniac, the first electronic computer,
which was located at the Ballistic Re-
search Laboratory, Aberdeen Proving
Ground. A summary of this work was
published in 1951 (US Department of
Commerce, Applied Mathematics, Se-
ries 12:19-20).

While carrying on her work at Ar-
gonne, she continued her voluntary
role at the University of Chicago by
lecturing to classes, serving on commit-
tees, directing thesis students, and par-
ticipating in the activities at the Insti-
tute for Nuclear Studies (now known as
the Enrico Fermi Institute). The uni-
versity had pulled together in this insti-
tute a stellar assembly of physicists and
chemists, including Fermi, Urey, and
Libby, as well as Teller and the Mayers,
Gregor Wentzel joined the faculties of
the physics department and institute
later, and the families quickly became
very close, one outcome being the join-
ing of the families by marriage of Ma-
ria Ann to the Wentzels’ son.

Subrahmanyan Chandrasekhar, who
had been on the faculty of the astron-
omy department for many years, also
joined the institute. A stream of young
and very bright physical scientists
poured into the institute, and the at-

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232

HISTORY OF PHYSICS

mosphere was stimulating to the ex-
treme. To add to this exciting atmos-
phere, which in some ways must have
been reminiscent of Gottingen in the
early days, her former teacher and
friend, James Franck, was already a
member in the university’s chemistry
department.

The activities in the institute reflect-
ed the interests of the leading lights,
interests that were very broad indeed,
ranging from nuclear physics and
chemistry to astrophysics and from cos-
mology to geophysics. The interdisci-
plinary character of the institute was
well suited to the breadth of her own
activities in the past, so that her Chi-
cago years were the culmination of her
variety of scientific experience. In
keeping with this, she turned her atten-
tion at first to completing and publish-
ing some earlier work in chemical phy-
sics, including work with Jacob
Bigeleisen on isotopic exchange reac-
tions. Bigeleisen had collaborated with
her in other work at Columbia Univer-
sity and at this time was fellow of the
institute. At the same time, she began
to give attention to nuclear physics.

The shell model

Among the many subjects being dis-
cussed at the institute was the question
of the origin of the chemical elements.
Teller was particularly interested in

this subject and induced Maria Mayer
to work with him on a cosmological
model of the origin of the elements. In
pursuit of data required to test any such
model, she became involved in analyz-
ing the abundance of the elements and
noticed that there were certain regular-
ities associating the highly abundant
elements with specific numbers of neu-
trons or protons in their nuclei. She
soon learned that Walter M. Elsasser
had made similar observations in 1933,
but she had much more information
available to her and found not only that
the evidence was stronger but also that
there were additional examples of the
effect. These specific numbers ultimate-
ly came to be referred to as “magic
numbers,” a term apparently invented
by Wigner.

When she looked into information
other than the abundance of the ele-
ments, such as their binding energies,
spins, and magnetic moments, she
found more and more evidence that
these magic numbers were in some way
very special and came to the conclusion
that they were of great significance for
the understanding of nuclear struc-
ture. They suggested the notion of
stable “shells” in nuclei similar to the
stable electron shells associated with
atomic structure, but the prevailing
wisdom of the time was that a shell
structure in nuclei was most unlikely

Other colleagues in-
cluded Harold Urey
(left), Edward Teller
(bottom left) and Hans
Jensen (below).

because of the short range of nuclear
forces as compared to the long-range
Coulomb forces holding electrons in
atoms. There was the further difficulty
that the magic numbers did not fit
simple-minded ideas associated with
the quantum mechanics of shell struc-
ture.

Maria Mayer persisted in checking
further evidence for shell structure,
such as nuclear beta-decay properties
and quadrupole moments, and in try-
ing to find an explanation in terms of
the quantum mechanics of the nuclear
particles. In this she was greatly en-
couraged by Fermi and had many dis-
cussions with him. She was also
strongly supported by her husband,
who acted as a continual sounding
board for her thoughts on the subject
and provided the kind of guidance that
could be expected from a chemist who,
in many ways, was better equipped to
deal with phenomena of this kind than
a physicist. The systematics of regular-
ities in behavior with which she was
faced had great similarity to the sys-
tematics in chemical behavior that had
led to the classical development of va-
lence theory in chemistry, and whose
fundamental explanation had been
found in the Pauli Exclusion Principle.

It was Fermi who asked her the key
question, “Is there any indication of
spin-orbit coupling?” whereupon she
immediately realized that that was the
answer she was looking for, and thus
was born the spin-orbit-coupling shell
model of nuclei.

Her ability to recognize immediately
spin-orbit coupling as the source of the
correct numerology was a direct conse-
quence of her mathematical under-
standing of quantum mechanics and
especially of her great facility with the
numerics of the representations of the
rotation group. This ability to identify
instantly the key numerical relation-
ships was most impressive, and even
Fermi was surprised at how quickly she
realized that his question was the key
to the problem.

Joseph Mayer gives the following
description of this episode:

Fermi and Maria were talking in
her office when Enrico was called
out of the office to answer the
telephone on a long distance call.
At the door he turned and asked
his question about spin-orbit cou-
pling. He returned less than ten
minutes later and Maria started to
‘snow’ him with the detailed expla-
nation. You may remember that
Maria, when excited, had a rapid-
fire oral delivery, whereas Enrico
always wanted a slow detailed and
methodical explanation. Enrico
smiled and left: ‘Tomorrow, when
you are less excited, you can ex-
plain it to me.’

While she was preparing the spin-

BIOGRAPHY

233

orbit-coupling model for publication
she learned of a paper by other physi-
cists presenting a different attempt at
an explanation and, as a courtesy, she
asked the editor of the Physical Review
to hold her brief letter to the editor in
order that it appear in the same issue
as that paper. As a result of this delay,
her work appeared one issue following
publication of an almost identical inter-
pretation of the magic numbers by Otto
Haxel, J. Hans D. Jensen, and Hans E.
Suess. Jensen, working completely in-
dependently in Heidelberg, had almost
simultaneously realized the impor-
tance of spin-orbit coupling for ex-
plaining the shell structure, and the
result had been this joint paper.

Maria Mayer and Jensen were not
acquainted with one another at the
time, and they did not meet until her
visit to Germany in 1950. In 1951 on a
second visit, she and Jensen had the
opportunity to start a collaboration on

further interpretation of the spin-or-
bit-coupling shell model, and this was
the beginning of a close friendship as
well as a very productive scientific
effort. It culminated in the publication
of their book, Elementary Theory of
Nuclear Shell Structure (1955). They
shared the Nobel Prize in 1963 for their
contributions to this subject.

After Fermi’s death in 1954, other
members of the Institute for Nuclear
Studies who had provided so much
stimulation for her left Chicago. Teller
had gone earlier in 1952, Libby left in
1954, and Urey in 1958. In 1960 she
accepted a regular appointment as pro-
fessor of physics at the University of
California at San Diego when both she
and her husband had the opportunity
to go there.

Her appointment as a full professor
in her own right at a major university
was very gratifying to her, and she
looked forward to the stimulation of

this newest interdisciplinary group of
scientists that was being drawn togeth-
er there. However, shortly after arriv-
ing in San Diego, she had a stroke, and
her years there were marked by contin-
uing problems with her health. Never-
theless, she continued to teach and to
participate actively in the development
and exposition of the shell model. Her
last publication, a review of the shell
model written in collaboration with
Jensen, appeared in 1966; and she con-
tinued to give as much attention to
physics as she could until her death in
early 1972.

* * *

This article was adapted from Biographical
Memoirs 50, The National Academy of Sci-
ences (1979).

References

1. Joan Dash, A Life of One’s Own (New
York: Harper and Row, 1973), page 231.

2. Ibid. □

234

HISTORY OF PHYSICS

Philip Morrisoi —

PHYSICS TODAY / AUGUST 1982

Valued for his scientific contributions to

the Manhattan Project, to theoretical physics and

to astrophysics, he has also contributed to

the public understanding of science and has been

one of the most thoughtful advocates of arms control.

Anne Eisenberg

When Philip Morrison, Institute Pro-
fessor at MIT, came to the Polytechnic
Institute of New York recently to give
the Sigma Xi lecture, a diverse group
attended. The group included physi-
cists, chemists, engineers; people who
admired Morrison for his sustained
fight against red-baiting in the 1950s
(in 1953 a national newsletter called
him “the man with one of the most
incriminating pro-Communist records
in the entire academic world”); and
people in the humanities who had en-
joyed his book reviews, films, articles
and textbooks. The diversity of the
audience reflected the diversity of
Morrison’s career.

Morrison is valued in the scientific
community for his gift of language, for
his wide-ranging intellect, and for his
ability to pull together insights from
different fields to shed light on a sub-
ject. Because he has spent considerable
time writing about science — explaining
and interpreting it for the public — he
exists also in the imaginations of people
outside science. He possesses what his-
torian Alice Kimball Smith has called1
a “rare sensitivity of spirit.”

His career has included Los Alamos
and Hiroshima in the 1940s, McCarthy-
ism in the 1950s, the Peace Movement
in the 1960s, and arms control from
1945 to the present. It began in Pitts-
burgh where he was reared and attend-
ed Carnegie Tech. After an initial
interest in radio engineering, he ma-
jored in physics, and went on to do his
doctoral work in theoretical nuclear
physics with Oppenheimer at the Uni-
versity of California at Berkeley. They
got along well; Morrison admired Op-
penheimer and reminisces today about
him: “There was only one difficulty
most of us had with Robert. You had to
be very careful with him, you couldn’t
give him too much of your problem, or
he would solve it before you.”

The Manhattan Project

Morrison had just gone to the Uni-
versity of Illinois at Urbana when the
war broke out. Hired by the Manhat-
tan Project, he went to Chicago to work
with Fermi, and stayed there until
1944. Morrison became leader of the
group that tested neutron multiplica-
tion in successive design studies for the
Hanford reactors.

Then, in 1944, he was recruited for
the Los Alamos effort by Robert
Bacher. Morrison worked at Los Ala-
mos in the group headed by Robert
Frisch, who, with his aunt Lise
Meitner, had pioneered in fission a few

BIOGRAPHY

235

years earlier. His job at Los Alamos
was to extend work done at Chicago at
which he was expert. “We made small
critical assemblies to test the neutron
behavior of the new plutonium and
uranium fission materials being pro-
duced at the main plants and shipped
to Los Alamos, in preparation for use in
the two bombs. Our job was to study
chain reactions in that stuff.”

It was here that Morrison and his
group did the famous experiments later
characterized by Feynman as “tickling
the dragon’s tail.” “No one had ever
made a chain reaction that had so
many prompt neutrons in it,” Morrison
comments. “All the chain reactions of
reactors are mediated in part by de-
layed neutrons; otherwise they aren’t
controllable at all. The bomb, on the
other hand, is made by fast, prompt
neutrons, which of course are uncon-
trollable.”

Morrison was concerned with build-
ing up experience on the passage from
the controlled state to the uncontrolled
state. This meant keeping the reaction
in a partially contained state under
active control, instead of relying on the
inherent stability of the system. “We
moved the system so carefully, but so
rapidly, that it had no chance to build
up on us — we hoped. We came very
close to making explosions, stopping
just in time. Feynman said this was
like tickling the tail of a dragon, and so
it was.”

In Disturbing the Universe, Freeman
Dyson characterizes2 the spirit of Los
Alamos as the “shared ambition to do
great things in science without any
personal feeling of jealousy.” Morrison
says that for himself the motivation
was not science, but victory over the
Germans.

In my group, two people died.
We had the feeling of front-line
soldiers with an important cam-
paign at hand.

To begin with, we felt we were
well behind the Germans. Rightly
or wrongly, we were seized by the
notion of this terrible weapon in
the hands of the Germans, whose
scientists we respected, admired,
and feared greatly because they
had been the teachers of our teach-
ers and colleagues.

We felt ourselves a little like the
English in 1940 — a small band
standing in the way. Could we
possibly beat them? At first there
was this terrible responsibility,
and then in the end we became

Anne Eisenberg teaches science writing at the
Polytechnic Institute ot New York in Brooklyn.

more and more flushed with the
fact that we had overcome them.
But it wasn’t a question of science.

It was one of victory. I remember
very well.

Morrison conveyed this atmosphere
to us with a story of John Wheeler in
Chicago: “When noontime came and
the 12:00 o’clock bell rang, most of us
would go to lunch at the nearby cafete-
ria. We’d learned, though, not to both-
er Wheeler. He brought his lunch and
when the bell rang he took it and his
Princeton notebook out. Then he went
ahead to do what he regarded as his
‘real work’. He was so conscientious he
would never do this during work hours,
only during lunch. And that was the
attitude at Los Alamos as well.”

The absorption in the immediate
task was complete. Only as work on
the bomb drew to a climax did Morrison
consider how it would be used against
the Japanese. “We knew there would
have to be a trial, but we thought
suitable conditions could be made. For
instance, I thought, as did many other
people, that there was going to be a
warning.” But no explicit warning was
given. The bomb was tested at Alamo-
gordo 16 July and used on Hiroshima 6
August. Morrison says, “The military
authorities rejected any demonstration
as impractical. They felt Japan would
not be deterred by the sight of a patch
of scorched earth in the desert. The
military had made up its mind. It
would have taken a very powerful po-
litical presence — one that wasn’t avail-
able— to sway them. The United States
therefore gave no explicit warning. I
think this was a moral failure.”

Was Morrison surprised the scientists
at Los Alamos were not more concerned
with the implications of the bomb they
were building? “Not at all. There was
much discussion about this in the labs,
quieter, of course, than those at the Met
Labs in Chicago. But we were seized
with a terrible responsibility, and our
leaders were trying to make sure our
attention was not diverted.”

After the Trinity test, Morrison, who
had been responsible for the design and
final deployment of the plutonium
core, again prepared and packed the
equipment, this time to go to the Mar-
iana Islands. When the bombs were
dropped on Japan he was on the island
of Tinian, from which the planes for
both atomic attacks set off.

He was among the first Americans to
visit Hiroshima after the war. “I had
earlier decided that the most useful
thing one could do would be to try to go
through the entire process as a histori-
cal witness.” At the invitation of Gen-

eral Thomas Farrell, assistant to Gen-
eral Leslie Groves, Morrison joined the
12-man group that went to Hiroshima
just 31 days after the explosion to
determine the effects of the atomic
bomb released by the Enola Gay. They
arrived in Yokohama the day after
MacArthur, and followed him to Tokyo.
“For me,” Morrison said in an inter-
view3 with Daniel Lang, “The first and
main impact of Hiroshima’s destruc-
tion had come . . . when we were flying
down there from Tokyo. First we flew
over Nagoya, Osaka, and Kobe, which
had been bombed in the conventional
manner, and they looked checkered —
patches of red rust where fire bombs
had hit intermingled with the gray
roofs and green vegetation of unda-
maged sections. Then we circled Hiro-
shima, and there was just one enor-
mous, flat, rust-red scar, and no green
or gray, because there were no roofs or
vegetation left.”

Morrison walked through the city
with Geiger counters and Lauritzen
electroscopes and aided by an inter-
preter, a guide, and a policeman. “It
had burst precisely at the spot we
wanted it to, high over Hiroshima.
There had been a minimum of radioac-
tivity.”

Arms control

After the war, Morrison returned to
the US to find himself at the heart of
the movement for international arms
control, whose advocates operated in
diverse ways — in arenas ranging from
guarded offices to hearing chambers
and press conferences at the Senate
Office Building; dispensing the mes-
sage through coded teletypes and
rushed press statements; disputing
with colonels and reconnaisance ex-
perts; persuading congressmen and re-
porters. A large number of concerned
scientists — many of them organized
into groups such as the Manhattan
Project Scientists, the Association of
Los Alamos Scientists, the Association
of Oak Ridge Scientists, Atomic Scien-
tists of Chicago — met in Washington in
the fall of 1945. Out of this meeting the
Federation of American Scientists was
eventually formed. The Federation be-
gan operating in January of 1946, with
Morrison as a member of the adminis-
trative committee.

Morrison described their original
goals to us:

We — the people the press soon

characterized as atomic scien-
tists— wanted to turn over techni-
cal details of bomb production to a

world authority under adequate

controls. We sought to prevent a

nuclear arms race by establishing
this worldwide authority.

The Federation believed that a continu-
ing monopoly of the atom bomb by the
United States was impossible. Without
staff or salary, Federation members
worked in Washington preparing re-
ports on how to establish a worldwide
atomic authority.

It seems to me that one finds in the
story two distinct ways of meeting
the sense of responsibility — in-
deed, of grave duty — that the Man-
hattan-project scientists as a whole
felt then and feel still.

One of these is the way of the
“insider.” Oppenheimer — lucid,
persuasive, wonderfully analyti-
cal— worked in secret with gener-
als and diplomats, trying in a thou-
sand ways to demonstrate what
the facts implied. Szilard lived by
the phone, buttonholing lobbyists
and becoming himself the lobbyist
par excellence. Both men acted
inside the government, personally
bringing their schemes before the
individuals who had power, who
wrote and passed laws.

And then there were the rest of
us: younger, less famous and less
able. Ours was the way of the
dissenter. In the way we acted
there was a sense less of knowledge
than of commitment. William Hi-
ginbotham, Joseph Rush, Louis Ri-
denour, John Simpson and scores
of others in Washington spoke and
wrote publicly for 3000 scientists
back home at the project laborato-
ries or crowding back into the uni-
versities, and also for the physi-
cists and chemists who had not
been in the project at all but felt
about as we did. From shabby
rented offices overcrowded and lit-
tered with mimeographed state-
ments and pamphlets the ‘atomic
scientists’ floated in the eddying
stream of American public opin-
ion.4

Morrison comments that “mutual de-
terrence was not the vision of 1946.
The scientists sought true stability
then, not metastability, not the top-
heavy balancing rock on which we all
breathlessly sit.”

Morrison played many roles during
the period, roles that called both upon
his fertile mind and upon his consider-
able ability as a speaker. He worked
for the Bulletin of the Atomic Scien-
tists, composed FAS policy drafts, and
appeared as a principal witness at hear-
ings on atomic bomb policy. He worked
on a report of ways to detect atomic
bomb laboratories, testing sites and
assembly plants. But no matter how
carefully he and others stressed how an
international authority could operate
under adequate controls — indeed, no
matter how many times they explained

what they meant by “under adequate
controls” — they were accused of want-
ing to give away the bomb.

The arms race that Morrison had
predicted grew as the scientists’ move-
ment for international controls waned
after 1946. Morrison, who joined the
faculty of Cornell University in 1946,
remained in the fight for international
arms control even as the public acclaim
for scientists began to ebb.

McCarthyism

He was soon in need of defense him-
self. As an undergraduate at Carnegie
Tech Morrison had joined the Commu-
nist Party, and he remained a member
when he went to graduate school at the
University of California at Berkeley, a
school known at that time for its free-
thinking, socialistic atmosphere. By
1941, Morrison was out of the party,
but his political activities continued.
At Cornell, he was deeply involved in
the Peace Movement and in a variety of
radical intellectual activities. It was
not the involvement that was so
noteworthy as much as the level of
activity: a continuous string of speech-
es and appearances made Morrison one
of the most politically active scientists
throughout the fifties.

During this period there were many
attempts to fire him. “What has Cor-
nell University done about Morrison?”
the right-wing newsletter Counterat-
tack asked5 in March 1953, answering
“Nothing!” In part the attempts were
foiled by his situation, because, as a
private school, Cornell was not quite as
vulnerable to pressure as public
schools. Nonetheless, considerable
forces were exerted on Cornell, where
his promotion from associate to full
professor was held up for so long that
the Physics Department began to talk
of refusing to submit any further pro-
posals for promotions until Morrison’s
was acted on.

His promotion finally became an is-
sue before the Cornell Board of Trust-
ees, who had him summoned. Even in
those times, with Morrison the center
of a series of attacks for such charges as
“urging clemency for the Rosenbergs,”
the trustees were charmed by Morri-
son’s intelligence and grace; they
granted his promotion.

Morrison was also called before Sena-
tor William Jenner’s Internal Security
Subcommittee, where he talked frank-
ly about himself and his early involve-
ment with the Communist Party with-
out naming other names; unsatisfied,
the subcommittee continued to pry.
For instance, they summoned another
physicist for a special security clear-
ance. This physicist was surprised but
somewhat flattered to be called for
special clearance. When he got there,
he was taken aback to discover the
committee had no interest in him; they

r

were only using the occasion as an
opportunity to pump him about Morri-
son.

Morrison spent 19 years on the Cor-
nell faculty before going to MIT. At
Cornell, Morrison was famous not only
for his social activism but also for his
teaching. “Phil’s a born teacher,” Dy-
son, who was a colleague of Morrison’s
at Cornell, comments. “Whenever one
didn’t know what to do with a student,
one sent the student along to Phil. He
had an infinite supply of patience.”
Dyson says that it often seemed as if
half the graduate students in the Phy-
sics Department were taken care of by
Morrison, who spent hours talking to
them, finding out which research ideas
they could tackle.

Astrophysics

It was while Morrison was at Cornell
that his interest turned from theoreti-
cal physics to astrophysics. “I was
always rather interested in astrophys-
ics,” he recalls. “As a graduate student
I published several small papers in
nuclear astrophysical problems with
Oppenheimer. At Cornell, though, I
was actually trying to be a nuclear
physicist until I took a sabbatical leave
in 1952.”

While on leave, Morrison determined
to work on some of Bruno Rossi’s prob-
lems; he knew Rossi’s work from their
days together at Los Alamos. “Along
with many other scientists in the cos-
mic-ray domain, the early 1950s found
me pushed into astronomy. The cos-
mic-ray people had always used this
natural phenomenon as a source for
high-energy particles — mesons were
first discovered in cosmic rays — but in
the early fifties machines became pow-
erful enough to rival cosmic rays.
Then, as machines improved, the cos-
mic rays were simply outcompeted. So
cosmic rays were no longer of central
interest from the point of view of their
intrinsic physics; the interest was more
in where they came from, first consid-
ering possible sources within the solar
system, and then beyond. That inter-
est gradually drew me and other scien-
tists farther and farther into astron-
omy.” He is pleased with the work he
did on the origin of cosmic rays. “I do
consider it as rather a high point. I
regarded myself as a specialist in cos-
mic rays during the 1950s. At that
time I proposed no single origin for
them, but instead suggested they were
highly hierarchical.” Morrison argued
that different places make different
cosmic rays and that the highest ener-
gy concentrations might come from
quasar-like objects such as the nearby
radio galaxy M87.

At Cornell Morrison worked with
Hans Bethe, a long-term friend and
supporter. In 1956 they wrote a text-
book together, Elementary Nuclear

Theory. “It was a useful and happy
collaboration,” Bethe says today. “He
has ideas which are not obvious. His
genius is to connect many different
parts of physics.” As an example,
Bethe cites Morrison’s discussion of the
radiogenic origin of the helium isotopes
in rocks. Morrison argued that the
ratio of helium-3 to helium-4 is much
greater in the atmosphere than it is in
rocks, because it rocks helium-4 comes
mainly from radioactivity, whereas in
the atmosphere there is relatively more
helium-3 produced by the cosmic ray-
mediated disintegration of nitrogen.
“It is a typical insight of Philip’s to
connect two opposite things — such as
cosmic rays and terrestrial radioacti-
vity— to determine the composition of
samples taken from such places as hot
springs.”

Morrison is known not only for his
ability to connect disparate elements,
but for his willingness to challenge
assumptions. His interpretation of
M82, once touted as an example of an
exploding galaxy, is one instance of this
characteristic. Morrison suggested
that what we were seeing is not an
explosion, but rather an intergalactic
dust cloud through which the galaxy is
passing, the interaction giving rise to
features that one might interpret as an
explosion. “Although M82 looks super-
ficially as though it were exploding in a
mini-quasarlike way,” Morrison com-
ments, “in fact it seems pretty clear it
isn’t at all.” Instead of there being one
point-like center — a tiny engine that
does everything for the device — the
central object is the whole core of the
galaxy, thousands of light years across,
in which hundreds, even thousands or
millions of new stars are suddenly
formed. “The rapid bursts of star for-
mations can create in some ways the
same kind of activity as if there were a
quasar-like object. In this case, how-
ever, the energy is primarily nuclear
instead of primarily gravitational.”

Paul Joss, a theoretical astrophysi-
cist at MIT, comments on Morrison’s
work: “Both with M82 and with his
supernova model, Morrison proposed
testable models that gave us something
to attack, challenging us and forcing us
to rethink.” Morrison’s supernova
model is an attempt to account for the
visible light that comes from superno-
vae “without worrying too much about
the causes of the explosion.” The cen-
tral idea of his theory is that the
observed light from the supernova con-
sists of two portions: those photons
that reach the observer directly along a
straight line and those that interact at
least once, travelling along a dogleg
path. Because the original outburst is
so brief, even the small delays that
arise from the somewhat greater
length of the dogleg path are signifi-
cant. Simple geometrical arguments

238

HISTORY OF PHYSICS

show that the locus of the secondary
emission points (places where light
from the supernova is absorbed and
then reemitted as fluorescence) form a
sequence of expanding ellipsoids whose
focal points are the point of the super-
nova outburst and the position of the
observer. Because fluorescence effi-
ciencies are typically a percent or less,
the total energy of the explosion is from
100 to 1000 times more than can be
detected on earth in the visible region.

Joss says, “Phil’s work on superno-
vae is a very good example of his impact
on astrophysics. He has a way of look-
ing at fundamental assumptions and
asking, ‘Why do we believe this?’ In
supernovae, for instance, there was a
standard picture, one that was prob-
ably right in a primitive sense, that is,
supernovae result from violent explo-
sions in massive stars, causing in turn
both a very large expulsion of matter
into interstellar space and a very large
amount of electromagnetic radiation.
But Phil noted that if you take a star
the size of the sun and blow it up, you
are not going to get a tremendous
amount of visible light. The energy
that comes out is 1010 or 1011 times the
luminosity of the sun, and if it radiates
as a blackbody, then that energy is not
going to come out as visible light, it is
going to come out as x rays. The
expansion of the exploding material,
increasing the size of the radiating
surface, won’t help either, because by
the time the material has expanded as
much as it has to — through several
orders of magnitude times its original
size — it will have undergone such adia-
batic cooling it will hardly radiate at
all. So the reason that one can see this
visible light has to be more complicat-

Vatican Conference on nuclei of galaxies,
1 970: Morrison, an unidentified priest,
Donald Osterbrock, Martin Rees and Edwin
Salpeter. (Courtesy of AIP
Niels Bohr Library.)

ed. What Phil did was come up with a
very specific model. It’s been contro-
versial, but that’s not the point. It was
a testable model that made specific
predictions and challenged astrophysi-
cists to reconsider some of their basic
assumptions about the supernova
phenomenon.”

Teaching

Morrison has been at MIT since 1964,
first as Francis Friedman Visiting Pro-
fessor, and then as a permanent faculty
member since 1965. Morrison’s inter-
est in educational theory influenced his
move to MIT. “Gerald Zacharias invit-
ed me to the school. He had an intense
interest in science education, an inter-
est he knew I shared.” MIT was a
center of educational innovation, and
Morrison was associated with the Phys-
ical Science Study Committee at its
inception and coauthor of its secon-
dary-school text Physics. Morrison, to-
gether with Don Holcomb of Cornell,
also wrote a physics text for college
students, My Father's Watch. Al-
though not widely used, it had a special
appeal to teachers introducing adults
to physics, perhaps because of Morri-

J. Robert Oppenheimer (left) and Major W.
A. Stevens in May 1 944, selecting a site
for the atomic-bomb test. (Photo by Kenneth
Bainbridge, courtesy AIP Niels Bohr Library.)

son’s care to relate scientific argu-
ments to history, art and philosophy.

Throughout Morrison’s career he has
interpreted science for the public in
popular articles, in science films, and in
monthly book reviews for Scientific
American. These book reviews in all
fields of science are particularly well-
known. One hundred years ago,
Charles Darwin wrote6 of the scientist
Robert Brown: “He was rather given to
sneering at anyone who wrote about
what he did not fully understand. I
remember praising Whewell’s History
of the Inductive Sciences to him, and he
answered, ‘Yes, I suppose that he has
read the prefaces of very many
books.’ ” Morrison is vulnerable to the
same sneer, yet few would comment so
of his incisive performances each
month in Scientific American. Instead,
one senses a polymath interested in
every nook and cranny, as Morrison
somehow makes his way through the
500 books he receives each month,
choosing and then reviewing thorough-
ly the handful he selects as interesting
and instructive.

“I judge my job to see what’s inside,
and then to unpack it. The nice part of
the book-review column in Scientific
American, and what makes it different
from others, is that I don’t need to
review all the important books. I am
not obliged to say, this is a lousy book
but we have to review it because it is
the work of an important author.”
Instead, Morrison tries to take a var-
iety of books representing either a good
popular approach or an approach at an
introductory level. The reviews — ser-
ious, generous, often more entertaining
than the original volumes — are a re-
flection of the intellectual energy that
consumes Morrison; they are also the
result of the peculiar ability he has to

BIOGRAPHY

239

read almost as rapidly as he can turn
pages.

Throughout Morrison’s book re-
views, books and films, there is a stress
on the evidence rather than on neatly
packaged conclusions or indeed on the
personality of the presenter. “The key
thing in a science film is to show the
evidence,” Morrison says, “but the me-
dia believe more in testimony and at-
mosphere.” Morrison tells an anecdote
to illustrate this conflict. In his film
“Whispers from Space,” which Morri-
son considers his best, he spends half
the program establishing and demon-
strating experiments that are at least
100 years old. For instance, to illus-
trate one of the most important fea-
tures of blackbody radiation, the
viewers see a kiln loaded with dishes
and piggybanks. These gradually heat
up until all detail is lost: first the dishes
disappear, then the piggybanks, until
the viewer is left with a bland, smooth
space. When the executive producer
saw the clip, he exclaimed, “You’re
spending all this time and money on a
thing you tell me was discovered 150
years ago. We can’t do that old-hat
stuff.”

Morrison comments, “So long as
science is seen largely as a personal
view, so long as science films have a
speaker who mainly ignores the evi-
dence and presents the history of
science as his own concoction of ideas
and insights, it is possible to talk of
Bermuda triangles and flying saucers.
It’s good enough if someone says it. If
you invent myths and don’t explain,
people can’t test the foundations of
your beliefs, or be prepared to change
when the foundation changes. Then
another myth comes along and beats
your myth. That’s how the creationists
can come along with their demands for
equal time: as far as they are con-
cerned, it is myth against myth.”

Essentially Morrison was a radical as
a youth and remains that way today.

His deep involvement in arms control
extends from 1945 to the present. Two
years ago he, his wife, and four Boston-
area colleagues published The Price of
Our Defense : A New Strategy for Mili-
tary Spending. The book aimed at
limiting the upward-spiraling arms
trade and thus lightening what Morri-
son calls “the thermonuclear sword
hanging over all mankind, sharper and
heavier each decade.” The authors
take a look at how much the US needs
to spend to maintain its national secu-
rity, and propose a program for de-
creasing land, sea and air forces to give
a “prudent military structure prepared
for eventualities short of all-out nu-
clear attack.” Against an all-out nu-
clear attack, the authors argue, there
can be no defense; one must rely on
deterrence alone.

How well has the book done? “The
Pentagon was interested,” Morrison
comments. “It sold quite well in book-
stores in Washington. It’s also been
popular with people in the peace move-
ment. But we are in a period when the
Russians are perceived as standing 10
feet tall. There are no signs that the
government is considering the nuclear-
arms cuts we proposed. In fact, it’s
quite the opposite.” Morrison contin-
ues to act as a gadfly to the defense
establishment with an energy charac-
teristic of all his political struggles.
One of his targets is the Air Force,
which he says is on the edge of obsoles-
cence. “Of course, it can’t accept that,
and so it tries harder. As the largest
industrial organization in the world, it
is up to all the sorts of things you would
expect from a huge organization that
cannot face its own obsolescence. The
MX system is a perfect example; its
chief value lies in its ability to keep the
Air Force in the strategic-missile busi-
ness.”

Morrison continues to have a deep
concern about nuclear weapons. “It is
one of the great failings of the Ameri-

can political process,” he says, “that
there is a huge hue and cry against
nuclear reactors, and nothing much
about bombs. I think to some extent
this had to do with displacement. Peo-
ple can’t deal with bombs, and they
displace their concern onto reactors,
which turn out to be vulnerable objects.
It’s a most important phenomenon, the
absence of attention to one, and the
irrational attention to the other. But
since the summer of 1981 I see a deci-
sive change.”

One of Morrison’s most striking char-
acteristics is the immense energy he
has spent writing about science for the
public. Why do this? “In part,” he
replies, “I think it is simply that I have
a flair for it. But I imagine it’s more
than that. I feel very keenly an obliga-
tion to maintain the social nexus in
which I’ve learned and become a scien-
tist. The one obligation society makes
on you is that you must explain your
craft, because that is the cultural trea-
sure you can pass on. People in the
future will need the information.”

References

1. A. K. Smith, A Peril and a Hope: The
Scientists’ Movement in America, 1945-
47, U. of Chicago P., Chicago (1965).

2. F. Dyson, Disturbing the Universe, Harp-
er & Row, New York (1979).

3. D. Lang, From Hiroshima to the Moon:
Chronicles of Life in the Atomic Age, Si-
mon & Schuster, New York (1959).

4. P. Morrison, Scientific American 213,
September 1965, page 257.

5. “Counterattack: Facts to Combat Com-
munism,” 6 March 1953, American Busi-
ness Consultants, Inc., 55 West 42 Street,
New York.

6. C. R. Darwin, Autobiography of Charles

Darwin, 1809-1882, Norton, New York
(1969). □

241

— Chapter 5

Personal Accounts

T T istory begins with senior people telling younger ones

J- what it was like back in the old days, and this remains
by far the most popular kind of history. At meetings of their
societies, physicists love to invite eminent people to speak
for half an hour or so on how they made their famous
discoveries. We find a peculiar fascination in every
circumstance surrounding the discoveries, perhaps
because the results have become dry facts embedded in
textbooks — so neatly built into the structure of science that
we could scarcely imagine what physics was like without
this knowledge, if the discoverers did not remind us. Some
of these recollections have found their way into PHYSICS
TODAY; that is the origin of nearly all the articles in this
section. From Einstein on relativity to Frisch and Wheeler
on fission, from Goudsmit and Uhlenbeck on electron spin
to Fermi on the early days of the neutron chain reaction,
with Livingston and McMillan on cyclotrons in between,
these first-person accounts take us into the hidden core of
the scientists’ work.

The AIP Center for History of Physics works to get tape
recordings of such reminiscences, and asks anyone holding
a memorial session to record the talks. The Center also
prompts reminiscence directly by conducting tape-
recorded oral history interviews, which are then
transcribed, edited, and indexed. The Center has over five
hundred such recordings in the archives of its Niels Bohr
Library, and these are frequently used by researchers. A
number of other programs and individual historians also

conduct interviews, saving for posterity the recollections of
physicists and astronomers.

Memory is notoriously fallible, and historians hesitate to
accept anything as fact simply because someone
remembers it as happening decades earlier. The AIP
Center for History of Physics and other programs strive to
secure documentary evidence, for example preserving
laboratory notebooks in permanent repositories or making
microfilms of unpublished correspondence, and historians
use these materials assiduously. It may also be possible to
check one person’s memory against another’s. In many
cases the documents or additional interviews tend to
support the original recollection; in other cases they do not.
Often there is simply no way to check, and the historian
must decide whether the story is internally consistent and
the speaker generally credible. For example, Frisch’s tale
of how he and Meitner thought of fission while walking in
the snow cannot be confirmed by other evidence, but it has
been accepted and repeated (with the stipulation that it is
simply a recollection) by many historians.

In any case there can be no doubt that reminiscence
contains an inner truth: the experience as it was
assimilated by a scientist who was on the spot. For
psychological understanding this may actually be more
accurate than the bare-bones documentary record. In some
fashion that is hard to describe, the first-person account
takes us closer than anything else to the living experience
of discovery.

Contents

243 How I created the theory of relativity
246 It might as well be spin

255 History of the cyclotron. Part I

261 History of the cyclotron. Part II

272 The discovery of fission

282 Physics at Columbia University

Albert Einstein
Samuel A. Goudsmit and
George E. Uhlenbeck
M. Stanley Livingston
Edwin M. McMillan
Otto R. Frisch and
John A. Wheeler
Enrico Fermi

I

PERSONAL ACCOUNTS

243

How I created
the theory of relativity

“The nose as a reservoir for
thoughts" cartoon by Ippei
Okamoto. (Courtesy AIP Niels
Bohr Library.)

Om «««^<» «

This translation of a lecture given in Kyoto on 14 December 1922
sheds light on Einstein’s path to the theory of relativity and offers
insights into many other aspects of his work on relativity.

Albert Einstein

Translated by Yoshimasa A. Ono

It is known that when Albert Einstein
was awarded the Nobel Prize for Phy-
sics in 1922, he was unable to attend
the ceremonies in Stockholm in Decem-
ber of that year because of an earlier
commitment to visit Japan at the same
time. In Japan, Einstein gave a speech
entitled “How I Created the Theory of
Relativity” at Kyoto University on 14
December 1922. This was an impromp-
tu speech to students and faculty
members, made in response to a re-
quest by K. Nishida, professor of philo-
sophy at Kyoto University. Einstein
himself made no written notes. The
talk was delivered in German and a
running translation was given to the

audience on the spot by J. Ishiwara,
who had studied under Arnold Som-
merfeld and Einstein from 1912 to 1914
and was a professor of physics at To-
hoku University. Ishiwara kept care-
ful notes of the lecture, and published*
his detailed notes (in Japanese) in the
monthly Japanese periodical Kaizo in
1923; Ishiwara’s notes are the only
existing notes of Einstein’s talk. More
recently T. Ogawa published2 a partial
translation to English from the Japa-
nese notes in Japanese Studies in the
History of Science.

But Ogawa’s translation, as well as
the earlier notes by Ishiwara, are not
easily accessible to the international

PHYSICS TODAY / AUGUST 1982

physics community. However, the ear-
ly account by Einstein himself of the
origins of his ideas is clearly of great
historical interest at the present time.
And for this reason, I have prepared a
translation of Einstein’s entire speech
from the Japanese notes by Ishiwara.
It is clear that this account of Einstein’s
throws some light on the current con-
troversy3 as to whether or not he was
aware of the Michelson-Morley experi-
ment when he proposed the special
theory of relativity in 1905; the account
also offers insight into many other
aspects of Einstein’s work on relativity.

— Y. A. Ono

244

HISTORY OF PHYSICS

It is not easy to talk about how I
reached the idea of the theory of
relativity; there were so many hid-
den complexities to motivate my
thought, and the impact of each thought
was different at different stages in the
development of the idea. I will not
mention them all here. Nor will I count
the papers I have written on this sub-
ject. Instead I will briefly describe the
development of my thought directly
connected with this problem.

It was more than seventeen years ago
that I had an idea of developing the
theory of relativity for the first time.
While I cannot say exactly where that
thought came from, I am certain that it
was contained in the problem of the
optical properties of moving bodies.
Light propagates through the sea of
ether, in which the Earth is moving. In
other words, the ether is moving with
respect to the Earth. I tried to find
clear experimental evidence for the
flow of the ether in the literature of
physics, but in vain.

Then I myself wanted to verify the
flow of the ether with respect to the
Earth, in other words, the motion of the
Earth. When I first thought about this
problem, I did not doubt the existence
of the ether or the motion of the Earth
through it. I thought of the following
experiment using two thermocouples:
Set up mirrors so that the light from a
single source is to be reflected in two
different directions, one parallel to the
motion of the Earth and the other
antiparallel. If we assume that there is
an energy difference between the two
reflected beams, we can measure the
difference in the generated heat using
two thermocouples. Although the idea
of this experiment is very similar to
that of Michelson, I did not put this
experiment to the test.

While I was thinking of this problem
in my student years, I came to know the
strange result of Michelson’s experi-
ment. Soon I came to the conclusion
that our idea about the motion of the
Earth with respect to the ether is incor-
rect, if we admit Michelson’s null result
as a fact. This was the first path which
led me to the special theory of relati-
vity. Since then I have come to believe
that the motion of the Earth cannot be
detected by any optical experiment,
though the Earth is revolving around
the Sun.

I had a chance to read Lorentz’s
monograph of 1895. He discussed and
solved completely the problem of elec-
trodynamics within the first [order of]
approximation, namely neglecting
terms of order higher than v/c, where v
is the velocity of a moving body and c is
the velocity of light. Then I tried to
discuss the Fizeau experiment on the

Yoshimasa A. Ono is a member of the re-
search staff of Hitachi Ltd. in Ibaraki, Japan.

Albert and Elsa Einstein embarking for the US on the S.S. Rotterdam, 1 921 , a year before their
trip to Japan. (Courtesy AIP Niels Bohr Library.)

assumption that the Lorentz equations
for electrons should hold in the frame
of reference of the moving body as well
as in the frame of reference of the
vacuum as originally discussed by Lor-
entz. At that time I firmly believed
that the electrodynamic equations of
Maxwell and Lorentz were correct.
Furthermore, the assumption that
these equations should hold in the ref-
erence frame of the moving body leads
to the concept of the invariance of the
velocity of light, which, however, con-
tradicts the addition rule of velocities
used in mechanics.

Why do these two concepts contra-
dict each other? I realized that this
difficulty was really hard to resolve. I
spent almost a year in vain trying to
modify the idea of Lorentz in the hope
of resolving this problem.

By chance a friend of mine in Bern
(Michele Besso) helped me out. It was a
beautiful day when I visited him with
this problem. I started the conversa-
tion with him in the following way:
“Recently I have been working on a
difficult problem. Today I come here to
battle against that problem with you.”
We discussed every aspect of this prob-
lem. Then suddenly I understood
where the key to this problem lay.
Next day I came back to him again and
said to him, without even saying hello,
“Thank you. I’ve completely solved the
problem.” An analysis of the concept
of time was my solution. Time cannot
be absolutely defined, and there is an
inseparable relation between time and
signal velocity. With this new concept,
I could resolve all the difficulties com-
pletely for the first time.

Within five weeks the special theory
of relativity was completed. I did not
doubt that the new theory was reasona-
ble from a philosophical point of view.

I also found that the new theory was in
agreement with Mach’s argument.
Contrary to the case of the general
theory of relativity in which Mach’s

argument was incorporated in the the-
ory, Mach’s analysis had [only] indirect
implication in the special theory of
relativity.

This is the way the special theory of
relativity was created.

My first thought on the general the-
ory of relativity was conceived two
years later, in 1907. The idea occured
suddenly. I was dissatisfied with the
special theory of relativity, since the
theory was restricted to frames of refer-
ence moving with constant velocity rel-
ative to each other and could not be
applied to the general motion of a

A Japanese Tea Ceremony. The Einsteins’
1922 trip included the usual tourist
attractions as well as scientific ones.

(Einstein Archives, courtesy AIP Niels Bohr

Library.)

PERSONAL ACCOUNTS

245

reference frame. I struggled to remove
this restriction and wanted to formu-
late the problem in the general case.

In 1907 Johannes Stark asked me to
write a monograph on the special the-
ory of relativity in the journal Jahr-
buch der Radioaktivitat. While I was
writing this, I came to realize that all
the natural laws except the law of
gravity could be discussed within the
framework of the special theory of
relativity. I wanted to find out the
reason for this, but I could not attain
this goal easily.

The most unsatisfactory point was
the following: Although the relation-
ship between inertia and energy was
explicitly given by the special theory of
relativity, the relationship between in-
ertia and weight, or the energy of the
gravitational field, was not clearly elu-
cidated. I felt that this problem could
not be resolved within the framework
of the special theory of relativity.

The breakthrough came suddenly
one day. I was sitting on a chair in my
patent office in Bern. Suddenly a
thought struck me: If a man falls
freely, he would not feel his weight. I
was taken aback. This simple thought
experiment made a deep impression on
me. This led me to the theory of gra-
vity. I continued my thought: A fall-
ing man is accelerated. Then what he
feels and judges is happening in the
accelerated frame of reference. I decid-
ed to extend the theory of relativity to
the reference frame with acceleration.
I felt that in doing so I could solve the
problem of gravity at the same time. A
falling man does not feel his weight
because in his reference frame there is
a new gravitational field which cancels

the gravitational field due to the Earth.
In the accelerated frame of reference,
we need a new gravitational field.

I could not solve this problem com-
pletely at that time. It took me eight
more years until I finally obtained the
complete solution. During these years
I obtained partial answers to this prob-
lem.

Ernst Mach was a person who insist-
ed on the idea that systems that have
acceleration with respect to each other
are equivalent. This idea contradicts
Euclidean geometry, since in the frame
of reference with acceleration Euclid-
ean geometry cannot be applied. De-
scribing the physical laws without ref-
erence to geometry is similar to
describing our thought without words.
We need words in order to express
ourselves. What should we look for to
describe our problem? This problem
was unsolved until 1912, when I hit
upon the idea that the surface theory of
Karl Friedrich Gauss might be the key
to this mystery. I found that Gauss’
surface coordinates were very mean-
ingful for understanding this problem.
Until then I did not know that Bern-
hard Riemann [who was a student of
Gauss’] had discussed the foundation of
geometry deeply. I happened to re-
member the lecture on geometry in my
student years [in Zurich] by Carl Frie-
drich Geiser who discussed the Gauss
theory. I found that the foundations of
geometry had deep physical meaning
in this problem.

When I came back to Zurich from
Prague, my friend the mathematician
Marcel Grossman was waiting for me.
He had helped me before in supplying
me with mathematical literature when

I was working at the patent office in
Bern and had some difficulties in ob-
taining mathematical articles. First he
taught me the work of Curbastro Gre-
gorio Ricci and later the work of Rie-
mann. I discussed with him whether
the problem could be solved using Rie-
mann theory, in other words, by using
the concept of the invariance of line
elements. We wrote a paper on this
subject in 1913, although we could not
obtain the correct equations for gra-
vity. I studied Riemann’s equations
further only to find many reasons why
the desired results could not be at-
tained in this way.

After two years of struggle, I found
that I had made mistakes in my calcu-
lations. I went back to the original
equation using the invariance theory
and tried to construct the correct equa-
tions. In two weeks the correct equa-
tions appeared in front of me!

Concerning my work after 1915, I
would like to mention only the problem
of cosmology. This problem is related
to the geometry of the universe and to
time. The foundation of this problem
comes from the boundary conditions of
the general theory of relativity and the
discussion of the problem of inertia by
Mach. Although I did not exactly un-
derstand Mach’s idea about inertia, his
influence on my thought was enor-
mous.

I solved the problem of cosmology by
imposing invariance on the boundary
condition for the gravitational equa-
tions. I finally eliminated the bound-
ary by considering the Universe to be a
closed system. As a result, inertia
emerges as a property of interacting
matter and it should vanish if there
were no other matter to interact with.
I believe that with this result the gen-
eral theory of relativity can be satisfac-
torily understood epistemologically.

This is a short historical survey of my
thoughts in creating the theory of rela-
tivity.

* ★ *

The translator is grateful to the late Profes-
sor R. S. Shankland for encouragement and
for informing him of reference 2.

References

1. J. Ishiwara, Einstein Ko-en Roku (The
Record of Einstein’s Addresses), Tokyo-
Tosho, Tokyo (1971), page 78. (Originally
published in the periodical Kaizo in
1923.)

2. T. Ogawa, Japanese Studies in the His-
tory of Science 18, 73 (1979).

3. R. S. Shankland, Am. J. Phys. 31, 47

(1963); 41, 895 (1973); 43, 464 (1974). G.
Holton, Am. J. Phys. 37, 968 (1972); Isis
60, 133 (1969); or see Thematic Origins of
Scientific Thought, Harvard U. P., Cam-
bridge, Mass. (1973). T. Hiroshige, Histor-
ical Studies in the Physical Sciences, 7, 3
(1976). A. I. Miller, Albert Einstein’s Spe-
cial Theory of Relativity, Addison-Wes-
ley, Reading, Mass. (1981). □

246

HISTORY OF PHYSICS

FIFTY YEARS OF SPIN

It might as well be spin

Compared to the competitive struggles of today’s highly specialized
physicists for recognition, the atmosphere in the “springtime of modern atomic

physics” was like that of a

Samuel A. Goudsmit

It was a little over fifty years ago that
George Uhlenbeck and I introduced the
concept of spin. The United States, cel-
ebrating its bicentennial, is only four
times as old as spin — not even an order of
magnitude older. It is therefore not
surprising that most young physicists do
not know that spin had to be introduced.
They think that it was revealed in Genesis
or perhaps postulated by Sir Isaac New-
ton, which young physicists consider to be
about simultaneous. There are many
other fifty-year mileposts in physics,
which also have been forgotten, such as
the radio-pulse experiments of Merle
Tuve and Gregory Breit that later led to
radar.

Restless as a willow in a windstorm

When we reach the stage in life in which
our future lies behind us, young people
always ask us to look back. Most of us do
not realize that we have reached that
turning point until we are far beyond it;
then looking back becomes a burden and
often painful. We have many regrets —
but never for what we did, always for what
we failed to do. We realize that we failed
to make use of many important opportu-
nities, and so our looking back lacks ob-
jectivity. You must keep this in mind as
you read this article, in which I propose to
describe the contrast between today and
the springtime of modern atomic physics,
which spanned approximately the years
from 1919 to the early 1930’s and took
place primarily in Europe.

Was it really springtime? In some re-
spects, yes. Many little shrubs were
planted that in fifty years grew into
powerful trees full of fruit-bearing
branches. Let me hasten to point out
that at the time of planting, it was im-

Samuel A. Goudsmit is visiting professor at the
Department of Physics of the University of Ne-
vada, Reno.

“Peyton Place without sex.”

possible to know which tree would flour-
ish, although in hindsight it appears that
some planters and observers made the
right guesses, just as at the races and in
the stock market.

Was it a romantic time? Were physi-
cists better off and happier than they are
today? Wasn’t it exciting in those revo-
lutionary years to have personally known
Albert Einstein, H. A. Lorentz, Niels
Bohr, Paul Ehrenfest, Arnold Sommer-
feld, Pieter Zeeman and many others?
The answer to all of these questions is, of
course, that at that time the young people
were not aware of or did not appreciate
the circumstances in which they lived. In
hindsight it must have been an unusually
interesting period, even for minor par-
ticipants. It is true that I was “restless as
a willow in a windstorm” and often
“starry-eyed and vaguely discontented”
and perhaps suffered from spring fever.
From an objective viewpoint however, it
was merely different from today’s physics;
the concept of the “good old days” does
not apply.

To describe the difference to those who
did not personally experience that period,
I must use analogies. The best analogy I
have found so far is to say that the present
community of physics represents life in a
modern metropolis, exciting and full of
frustration and dangers. In the 1 920’s, by
comparison, we lived in a small village
with its little feuds, a Peyton Place with-
out sex. I am sure that the present gen-
eration would not have liked it, most of all
because physics and physicists were un-
important to the outside world. The
press did not care, the government did not
care, the military did not care; isn’t that
awful? What is even worse, no one got his
expenses paid for giving a paper at a
meeting.

Marie Curie and Einstein were excep-
tions in that they had news value. Ein-
stein knew how to capitalize on his fame.

PHYSICS TODAY / JUNE 1976

Once, when Ehrenfest asked him why he
had gone to Spain where there was no
physics of interest to him, Einstein an-
swered, “True, but the King gives such
nice dinner parties.” In general, publicity
was frowned upon and many of Einstein’s
friends tried to persuade him to shun the
press. The photograph of 1923 on the
opposite page was not taken because
Einstein was visiting in Leiden, but be-
cause Douglas Hartree happened to pass
through. It shows also how small the
number of physicists was: It represents
the complete class of Ehrenfest. Only
half of these students were physicists, the
rest were astronomers and chemists.

Starry-eyed and vaguely discontented

To become a physics student in Europe
was an anomaly in the 1920’s. Physics
was not a profession but a calling, like
creative poetry, music composition or
painting. I was considered a failure by
my family. They expected me to become
a businessman, as anybody who worked
for a paycheck was considered a weakling.
Almost all students I met came from ac-
ademic families — their education came
from the home, their training from the
schools. As a physics student, I was
considered a sort of misfit. This is quite
different from what I found when I came
to the US, and especially from the situa-
tion today. Physics is now a profession,
like engineering or television repair, and
physicists come from all walks of life. In
Europe in the 1920’s it was rather difficult
to become a physicist. But once accepted
as a serious research student, one had
fairly easy access to the big shots in the
field, easier than at present.

I never understood why relativity, such
an abstract and difficult subject, caught
the interest of the general public. World
War I was followed by years of very severe
economic problems, uncertainties and
political upheavals in many areas. We

PERSONAL ACCOUNTS

247

are living again in such a period of inse-
curity and again we see an increased
public interest in the abstract, the occult,
in extrasensory experiences and the Loch
Ness monster. It scares me especially
because this time the lunatic fringe in-
cludes some physicists. One of them was
so taken in by the spellbinding, spoon-
bending Uri Geller that he wrote a book
about it. The world has lost confidence
in scientific and rational reasoning;
physics is now hard to sell.

It was in that old protected atmosphere
that George Uhlenbeck and I came up
with the concept of electron spin. The
number of active physicists was small, and
since I had already published several pa-
pers on spectra and atomic energy levels,
I was personally acquainted with several
of them. But I did not think spin im-
portant enough to send any of them pre-
prints or to write to them about it. I did
not worry at all about being scooped.
This had happened to me a couple of

times with work on spectral lines, but
there was so very much left to do that it
was merely a disappointment, not a ca-
tastrophe.

Personally the spin solution gave me
pleasure but not excitement. I did not
appreciate its possible significance until
Bohr showed such a great interest in it.
There were other items in my physics
work that gave me more of a thrill — for
example the first experimental determi-
nation, together with Ernst Back in Tii-

Spin, Leiden University and all that. The class of Paul Ehrenfest (near
the center) stands in front of the door of the Institute for Theoretical
Physics at the University of Leiden, probably in 1923. Albert Einstein
stands in the doorway, but the reason for the picture was a visit by Douglas
Hartree (between Einstein and Ehrenfest). The author, Sam (then Sem)

Goudsmit, is on the right. Jan Tinbergen (left, no hat) switched fields after
obtaining his PhD in physics, and received a Nobel Prize in economics.
The tall man next to Ehrenfest is Gerhard Dieke, who later became
physics chairman at Johns Hopkins. The woman beside Einstein is Ini
Roelofs; Jaap Voogt and Bernard Polak are fourth and fifth from left.

248

HISTORY OF PHYSICS

bingen, of a nuclear spin, that of bismuth.
There was of course no such thing as a
press conference when we discovered
electron spin. For me there were no job
offers either, not even as a high-school
teacher.

Today, a new bump in a curve is enough
to call Walter Sullivan of The New York
Times out of bed to make sure that the
work will get a headline in the paper.
Today competition is fierce and often
ruthless, because so much is at stake.
Funding, promotion and a whole career
may depend on publicity and on the
Citation Index. In the 1920’s, competi-
tion and animosities could be strong too,
and sometimes affected careers, but
funding was a minor consideration.
There were very few academic openings
and political considerations often deter-
mined who was chosen to fill them.

The published correspondence between
Einstein and Max Born shows how diffi-
cult it was for Jews to get jobs in Germany
long before Hitler came to power. The
same was true over here, at many, but not
all, universities and industrial laborato-
ries. When my former student Robert F.
Bacher was considered for a position at
Cornell University in 1934, R. C. Gibbs
asked me in confidence, on behalf of F. K.
Richtmyer, whether Bacher was Jewish —
if so, he would not have got the job. Some
of these animosities had an international
character, an aftermath of World War I.

The German physicist Sommerfeld

published his great and influential book
on atomic structure in 1921. It contained
a chapter about radioactivity, which did
not mention the Curies. The French
were obviously offended. However, in
those days the work of the Curies was
considered not physics but chemistry and
I very much doubt that Sommerfeld had
deliberately omitted their name. But
when the Dutch physicist Dirk Coster
sent Sommerfeld a manuscript on x-ray
energies for an opinion, he kept it so long
that one of his own pupils, Walter Kossel,
was able to scoop Coster. Similarly, on a
visit to Holland, Sommerfeld learned that
I was working on the spectrum of iron.
He made sure that his pupil Otto Laporte
got his results published first, making my
efforts obsolete. A professor protected
his pupils more than himself. These are
just examples of common quibbles, minor
compared to today’s frantic races for a
Nobel Prize.

It is sometimes pathetieto observe the
present almost violent striving for pub-
licity. The biochemist Erwin Chargaff
describes it pointedly for his field and
states: “That in our days such pygmies
throw such giant shadows only shows how
late in the day it has become.1 What
Chargaff overlooked is that pygmies also
throw large shadows at dawn. This could
be applied to me and several others in the
1920’s, the dawn of the new physics. It is
late in the day for physics too, but I am
not going to predict the future — I leave

PHOTO: A. PAIS. ROCKEFELLER UNIVERSITY

that to astrologers and computer addicts.
Fortunately there are still and will always
be a core of physicists who pursue their
science for its great intrinsic value only.
They love to teach and are not overanx-
ious to burst into print and publicity with
subliminal results and half-digested ideas.
We can recognize their work because the
adjective “beautiful” applies to it.

There are many colleagues who believe
that we received the Nobel Prize for in-
troducing electron spin. In fact, Lee
DuBridge recently introduced me as an
early Nobel Prize winner; I have also seen
it in print. That is all very flattering but
does not supplement my TIAA pension.
About thirty years after introducing spin,
we got the Research Corporation Award
and shared $2500; the following recipients
received $10 000. Again ten years later,
we each received the Max Planck Medal
from the German Physical Society. The
Nobel Prize was not for us — there were
too many physicists who made more im-
portant contributions at that time. For
example, such spectacular advances as the
explanation of radioactivity by George
Gamow, Edward Condon and R. W.
Gurney and that of chemical binding by
Walter Heitler and Fritz London were not
considered worthy of the award. Even
the theory of relativity was ignored; Ein-
stein was awarded the Nobel Prize for his
explanation of the photoelectric effect.
The discovery of spin was the main factor
for our being offered, in 1926, jobs at the
University of Michigan as instructors.
That was for me a far more significant
award than a Nobel Prize.

Busy as a spider spinning daydreams

This brings me to another difference
between the 1920’s and today: the ra-
pidity of change. As a young student I
was totally oblivious of possible changes.
As in my theme song, “I was as busy as a
spider spinning day dreams.” When
Sommerfeld’s book appeared I literally
believed that being cited in one of its
footnotes meant immortality. I have
forgotten whether I made it in a later
edition! The book has been obsolete for
decades. Another dream was some day
to be the successor of Zeeman at the
University of Amsterdam and continue
experiments on spectra and the Zeeman
effect. Years later when I was offered the
position, that area of physics was dead. I
did not take the job. Though changes did
occur in the 1920’s, one could follow them
more easily than today, in almost all of
physics. Today, extreme specialization
is a necessity for a physicist who wants to
make a meaningful contribution. The
different branches of modern physics now
speak different languages; each uses its
own jargon, unintelligible to those work-
ing in other areas.

The present generation is hardly aware
that we are living in a time of rapid
change, of revolution. A physicist’s work
may be forgotten or considered as be-

The originators ot the concept of spin, George Uhlenbeck (center) and Samuel Goudsmit (right),
are together, in 1926, with Oskar Klein, a Swedish physicist. Klein, who had spent the previous
year at the University of Michigan, was responsible for their being invited to teach there.

PERSONAL ACCOUNTS

249

longing in the public domain after two
years instead of after fifty years. I did my
best to adapt our journals' to the
present-day hectic activities, for example
by creating Physical Review Letters.
But that is not enough. The Physical
Review has to change further also. That
journal reminds me of an old mansion,
still inhabited by remnants of a family
that gradually has lost its fortune and its
servants but clings to outer appearances.
The physics community clings to the
journal’s format, which is too impressive
a facade for contents no longer very im-
pressive. Just read almost any article in

the Physical Review of the 1920’s and
1930’s to see the difference.

Now a final remark. Many young
people believe erroneously that wisdom
comes with age. On the contrary, age
brings fear of novelty and progress, fear of
loss of status. Almost forty years ago I
listened to the great Arthur Eddington
lecturing about the fine-structure con-
stant, 137. The little I understood was
obviously farfetched nonsense. I asked
my older friend, H. A. Kramers, whether
all physicists went off on a tangent when
they grew older. I was afraid. “No,
Sam,” answered Kramers. “You don’t

have to be scared. A genius like Ed-
dington may perhaps go nuts, but a fellow
like you just gets dumber and dumber.”

* * *

This article is an adaptation of a talk pre-
sented 2 February at the joint New York
meeting of The American Physical Society
and the American Association of Physics
Teachers as part of a symposium celebrating
the 50th anniversary of the discovery of elec-
tron spin.

Reference

1 E. Chargaff, Science 172, 637 (1971). O

FIFTY YEARS OF SPIN

Personal reminiscences

How one student who was undecided whether to pursue a career in
physics or history and another who had not taken his mechanics exam came to
identify the fourth atomic quantum number with a rotation of the electron.

George E. Uhlenbeck

In a one-page Letter to the Editor of
Naturwissenschaften dated 17 October
1925, Samuel A. Goudsmit and I proposed
the idea that each electron rotates with an
angular momentum h/2 and carries, be-
sides its charge e, a magnetic moment
equal to one Bohr magneton, eh/2mc.
(Here, as usual, h is the modified Planck
constant, m the mass of the electron and
c the speed of light.) Sam, in his accom-
panying article, tells something of those
times, fifty years ago. We have often
talked about the circumstances that led
to our idea, but it was mainly Goudsmit’s
recollections that have appeared in print
before now — they are, however, not
readily accessible in English.1'2'3 Al-
though I gave a short account4 of the dis-
covery of the spin as a part of my inau-
gural address for the Lorentz professor-
ship in Leiden in 1955, it therefore ap-
pears to be my turn to reminisce.

I am a bit reluctant to do this; first,
because my memories differ only in em-
phasis and in a few details from Sam’s
recollections, and second, because to de-
scribe the personal relationships and the
circumstances properly requires, I think,
almost an autobiography! However,
since this is of course not meant to be a
contribution to the history of the great
consolidation of the quantum theory in
the 1920’s, I will just try to tell my side of
the story, for what it is worth.

Note that I do not use the modish

Sonderdruck aus Die Naturwissenschaften. 13.Jahrg., Heft 47

(Verlag von Julius Springer, Berlin W g)

Ersctzung der Hypothese vom unmcchanischen
Zwang durch eine Forderung beztiglich des
inneren Verhaltens jedes einzelnen Elektrons.

§ i. Bekanntlich kann man die Struktur und das
magnetische Verhalten der Spektren eingehend be-
schreiben mit Hilfe des LxND&schen Vektormodelles R,
K. J und m1). Hierin bezeichnet R das Impulsmoment
des Atomrestes — d. h. des Atoms ohne das Leucht-
elektron — K das Impulsmoment des Leuchtelektrons,
J ihre Resultante und m die Projektion von J auf die
Richtung eines «LuBeren Magnetfeldes, alle in den ge-
br&uchlichen Quanteneinheiten ausgedriickt. Man muB
dann in diesem Modell annehmen:

a) daB fttr den Atomrest das Verh&ltnis des magne-
tischen Momentes zum mechanischen doppelt so groB
ist, als man klassisch erwarten wiirde.

b) daB in den Formeln, wo R *, K *, J* auftritt, man
diese durch R* — \ , K* — » , J* — J ersetzen muB. [Die
HEiSENBERGsche Mittelung8)] .

Dieses Modell hat sich iuBerst fruchtbar gezeigt
und hat u. a. geftihrt zur Entwirrung der verwickeltesten
Spektren.

§ 2. Man stoBt aber auf Schwierigkeiten, sobald man
versucht, das LANDfcsche Vektormodell anzuschlieBen
an unsere Vorstellungen iiber den Aufbau des Atoms
ans Elektronen. Z. B. :

a) Pauli8) hat schon gezeigt, daB bei den Alkali-
atomen der Atomrest magnetisch unwirksam sein muB.
da sonst der EinfluB der Relativitatskorrektion eine
Abhangigkeit des ZEEMANeffektes von der Kernladung
verursachen wiirde, welche in diesen Spektren nicht
wahrgenommen ist.

b) Beim LANDfeschen Modell darf man das Impuls-
moment des Atomrestes nicht mit demjenigen des
positiven Ions identifizieren, sowie man es nach der
Definition des Atomrestes erwarten wiirde. [Ver-
zweigungssatz von Land6-Heisenberg4) — un-
mechanischer Zwang],

c) Bei einigen in der letzten Zeit mit Hilfe des
LANDfeschen Schemas analysierten Spektren (z.B. Vana-
dium, Titan) stimmte das K des Grundtermes gar nicht
mit dem Werte, welchen man aus dem Bohr-Stoner-
schen periodischen Systems erwarten wiirde.

§ 3. Die obengenannten Schwierigkeiten zeigen alle
in dieselbe Richtung, namlich, daB die Bedeutung, wel-
ch ” • vD^schen Vektoren zukennt, wahr-

•-«. p**- hat schon einen

11 an Schwie*"'

§ 4. In beiden Auffassungen bleibt jedoch das Auf-
treten des sog. relativistischen Doubletts in den Ront-
gen- und Alkalispektren ein Ratsel. Zur Erklarung die-
ser Tatsache kam man in letzter Zeit zur Annahme einer
klassisch nicht beschreibbare Zweideutigkeit in den
quantentheoretischen Eigenschaften des Elektrons1).

§ 5. Uns scheint noch ein anderer Weg offen. Pauli
bindet sich nicht an eine Modellvorstellung. Die jedem
Elektron zugeordneten 4 Quantenzahlen haben ihre
urspriingliche LANDfesche Bedeutung verloren. Es liegt
vor der Hand, nun jedem Elektron mit seinen 4 Quan-
tenzahlen auch 4 Freiheitsgrade zu geben. Man kann
dann den Quantenzahlen z.B. folgende Bedeutung geben :

n und k bleiben wie friiher die Haupt- und azimu-
thale Quantenzahl des Elektrons in seiner Bahn.

R aber wird man eine eigene Rotation des Elektrons
zuordnen8).

Die iibrigen Quantenzahlen behalten ihre alte Be-
deutung. Durch unsere Vorstellung sind formell die
Auffassungen von Land6 und Pauli mit all ihren Vor-
teilen miteinander verschmolzen3). Das Elektron muB
jetzt die noch unverstandene Eigenschaft (in § 1 unter a
genannt), welche Land£ dem Atomrest zuschrieb,
iibernehmen. Die nahere quantitative Durchfiihrung
dieser Vorstellung wird wohl stark von der Wahl des
Elektronenmodells abhangen. Um mit den Tatsachen
in Ubereinstimmung zu kommen, muB man also diesem
Modell die folgenden Forderungen stellen:

a) Das Verhaitnis des magnetischen Momentes des
Elektrons zum mechanischen muB fur die Eigen-
rotation doppelt so groB sein als fur die Umlaufs-
bewegung4).

b) Die verschiedenen Orientierungen vom R zur
Bahnebene (oder K) des Elektrons muB, vielleicht in
Zusammenhang mit einer HEisENBERG-WENTZELschen
Mittelungsvorschrift5), die Erkl&rung des Relativitkts-
doubletts liefern konnen.

G. E. Uhlenbeck und S. Goudsmit.

Leiden, den 17. Oktober 1925.

Instituut voor Theoretische Natuurkunde.

*) W. Heisenberg, Zeitschr. f. Phys. 32, 84 1. 1925.

*) Man beachte, daB man die hier auftretenden
Quantenzahlen des Elektrons den Alkalispektren ent-
nehmen muB. R hat also fur jedes Elektron nur den
Wert 1 (in LANDfescher Normierung).

3) Z. B. wird nun auch die Bedeutung des Heisen-

RR* 0 1,',ma III • ■*r . worin

George E. Uhlenbeck is professor emeritus of The spin hypothesis was proposed in this Letter, which might never have seen the light of day
physics at The Rockefeller University, New York. because of objections based on a rigid-electron model, but it was too late to withdraw it.

250

HISTORY OF PHYSICS

words “revolution” or “breakthrough.” It
was really a consolidation of many lines of
thought, which admittedly occurred in the
rather short period say from 1923 till
1928, but which required about twenty
years of preparation. It will be a great
but very difficult task to write a proper
history about this period. Sam1 is very
skeptical about it and perhaps one must
wait till more materials (such as the let-
ters of Wolfgang Pauli) become available.

I will not go into the priority question.
Sam has told all about this, especially in
his Delta article,3 and I agree with his
conclusions. However, a short contri-
bution by E. H. Kennard should be men-
tioned.4 We were clearly not the first to
propose a quantized rotation of the elec-
tron, and there is also no doubt that Ralph
Kronig anticipated what certainly was the
main part of our ideas in the spring of
1925, and that he was discouraged mainly
by Pauli from publishing his results. In
the memorial volume to Pauli, Kronig has
written an article about the crucial period
1923-25, in which he also describes his
personal experiences.6 In the same vol-
ume there is a very useful survey by Bartel
van der Waerden,7 in which especially
Pauli’s contributions are discussed. Both
articles are at most only mildly critical
about Pauli’s attitude about the spin hy-
pothesis, and van der Waerden says ex-
plicitly that in his opinion Pauli and
Werner Heisenberg can not be blamed for
not having encouraged Kronig to publish
his hypothesis. I do know, however, from
a long conversation with Pauli in the
1950’s during a summer school in Les
Houches, that he blamed himself about
the whole episode — “Ich war so dumm
wenn ich jung war!’’ (“I was so stupid
when I was young!”) All I think one can
say is that our proposal came just at the
right time, that we had perhaps a better
appreciation of its consequences — espe-
cially with respect to the fine structure of
hydrogen — and, finally, that we had the
luck and the privilege to be students of
Paul Ehrenfest. His role in the story will
become clear in the following.

Switching to paradise

Let me begin my story with some au-
tobiographical notes. In September 1918
I started at the Technical University in
Delft as a student in chemical engineer-
ing. I wanted to study physics and
mathematics, but I did not have the
classical education that the law required
for admission to study at the University
in Leiden. The work at Delft was very
busy and disciplined. Every afternoon I
worked in the chemical laboratory, which
I especially disliked, probably because I
was not very good at it.

In January 1919, the law was changed,
thank God; the new so-called “Limburg
law” (I will never forget the name!) al-
lowed barbarians like me to study the
sciences and medicine at the universities.

I persuaded my parents to let me switch

This diagram from the 1926 Letter to Nature
illustrates how the spin hypothesis changes the
explanation of the fine structure of hydrogen-like
spectra. The principal quantum number is
three; the dotted lines are the levels without spin.
The new levels are at the same places as in the
Sommerfeld theory, but the earlier disagree-
ments with the correspondence principle have
been resolved by using the concept of spin.

to Leiden, which was easy because no
additional tuition was required — I only
had to change my commuter ticket from
Delft to Leiden. I lived at home with my
parents in The Hague.

I found Leiden a kind of paradise. We
had to take only five lectures a week and
one afternoon of a rather standard physics
laboratory. There was a wonderful
physics and mathematics library, the so-
called “Bosscha Reading Room” of which
Ehrenfest was the director. In physics
there were three professors. In addition
to Ehrenfest there was H. Kamerlingh
Onnes, the famous director of the low-
temperature laboratory, and Johannes
Kuenen, a very fine man, who gave the
first-year courses. There were few stu-
dents (in my year only four) and we all
knew each other. And, to top it all, there
were long vacations!

Since my high-school years I had been
especially interested in the kinetic theory
of gases, because to me it appeared to be
a theory that really explained the ob-
served phenomena. In all the free time I
had, I therefore studied Boltzmann’s
Vorlesungen iiber Gastheorie. It was
hard going; I had to learn analytical me-
chanics and several branches of mathe-
matics just to be able to follow the argu-
ment. But I really did not understand
what it was all about. I also dipped into
Gibbs’s Statistical Mechanics, with the
same experience. It was therefore a rev-
elation for me when I got hold of the fa-
mous Encyclopedia article of Paul and
Tatiana Ehrenfest. Suddenly it became
clear what the basic problems were and
what had been achieved by the founders
of statistical mechanics. There were a

whole series of open problems and ques-
tions, which showed the so-called “fron-
tier” of the subject. Of course it did not
occur to me to try to answer some of these
questions — I did not have the chutzpah!
I was a conscientious student and I
thought that I had to study all the books
before trying to do anything new.

In these years I hardly knew Goudsmit,
who was two years younger and was
therefore just coming over the horizon. I
also had little contact with Ehrenfest. He
knew that I existed, and once in a while he
looked over my shoulder to see what I was
studying. But I was too shy to ask him
questions, which was almost a prerequi-
site for talking to him! All this changed
completely after I had passed my so-
called “candidate’s examination” (roughly
equivalent to the BS degree), which as a
conscientious student I did in the re-
quired time (December 1920).

That year I also began to follow
Ehrenfest’s lectures, and was also allowed
to come to the famous Wednesday collo-
quium. I have described Ehrenfest’s
methods of teaching elsewhere,8 so not to
go too far afield let me just say here that
I remember those wonderful years espe-
cially because of the friendliness and
feeling of community of the whole group.
There was no competition. And this all
came from Ehrenfest. He taught us that
physics was not only fascinating but also
fun, something we should share with each
other. He had not a grain of pompous-
ness, a trait that was (and still is!) rare
among professors. We now know that,
already in those years, he struggled with
his feeling of inadequacy and with periods
of depression, but he never showed it to
us. I still remember his jokes and his
laughter!

The years in Rome

For me the only trouble was that, to
earn money, I accepted a job in my fourth
year. I taught mathematics, ten hours a
week, at the high school in Leiden. I did
not mind the teaching, but I had trouble
keeping order in my classes, and I be-
grudged the time it took. I did not get
much sympathy from my father, who
pointed out that, as I knew, even with a
doctor’s degree all I could expect was a job
as a high-school or gymnasium teacher in
some Dutch town. As he said, “Tu I’as
uoulu, George Dandin”! (“You wanted
it, George Dandin.”) When Ehrenfest
asked in class, some time in the spring of
1922, whether anybody was interested in
a tutoring job in Rome for a couple of
years I immediately raised my hand.
Thus began my Roman period, which al-
most changed the course of my life.

Since all this is meant to be an intro-
duction to the wonderful summer of 1925
when Sam and I worked together, I will
try to keep it short. My job in Rome,
about ten hours a week, was to teach the
youngest son of the Dutch ambassador, J.
H. van Royen, all the subjects required in

PERSONAL ACCOUNTS

251

a Dutch gymnasium except the classical
languages and history, for which there was
a second tutor and which took the rest of
the boy’s time. Every summer the boy
and I went back to Holland, where he was
tested to see whether he was ready for the
next grade in school. And so it went for
three years.

I had never been outside Holland since
my sixth year, so it was a real adventure
for me. I got a princely salary, and except
for studying the textbooks to keep ahead
of my student, I did not have much to do.
The first year I started to take Italian
lessons, which I kept up in the following
years. This was the most intelligent thing
I did in those days, and I am still proud of
it. The first year I also studied hard for
my doctoral examination, which (again as
a conscientious student) I passed in the
required time (September 1923). After
that time I became more and more inter-
ested and involved in the cultural history
of Italy. I travelled a lot (I could afford
it!) and I always took part in the activities
of the Dutch Historical Institute in Rome.
My first paper was a biographical sketch
of the Dutch philosopher Johannes
Heckius, who was one of the founders of
the Academia dei Lincei in Rome.9

I still tried to study the old Bohr-
Sommerfeld quantum theory, using the
dissertation of Jan Burgers, and I kept in
touch with Ehrenfest during the summer.
In 1923 I also met and became good
friends with Enrico Fermi, who was al-
ready at that time an accomplished
physicist. Still, even his influence did not
turn me back to physics. I suppose I went
through what nowadays is called an
identity crisis. Anyway, when I came
back in June 1925, 1 thought that my real
interest was in the study of cultural his-
tory, and that perhaps I should forget
about physics. I had a long talk with my
uncle, C. C. Uhlenbeck, the professor of
linguistics at Leiden, who was the wise
man in our family and who knew me very
well. He was sympathetic and he shared
my enthusiasm for the historian Johan
Huizinga. But he reminded me that if I
was serious I had better start to learn
Latin and Greek, and he gave me the good
advice first to try to finish my studies,
especially since I had never done any work
in physics by myself. Of course I also
talked with Ehrenfest, who somehow still
had enough confidence in me to propose
that we work together on a study of the
various solutions of the wave equation in
n dimensions; this later appeared in a
joint paper in the Proceedings of the
Dutch Academy.10 But he also told me
that I had better start learning what the
real problems in physics were, and that he
would ask Sam Goudsmit to teach me
what he knew and had done about the
theory of atomic spectra.

The riddle of the gyromagnetic ratio

Thus began the remarkable summer of
1925. Two days a week I went to Leiden

H. A. Lorentz makes a point. The grand old man of Dutch physics was skeptical of spin; according
to his calculations the velocity of the electron's surface was ten times the speed of light.

to work with Ehrenfest on the wave
equation and on the other days Sam and
I got together in The Hague to talk about
the recent developments of atomic theory,
which as I then slowly began to realize was
at that time (1923-25) the “frontier” of
physics.

At this point I think I should tell more
about Sam Goudsmit, especially since in
his accounts1’2'3 he speaks rather depre-
catingly about himself. It is true that
Sam was not a very conscientious student
and that he often had trouble passing the
required examinations in the subjects that
did not interest him. But on the other
hand he was a very independent worker.
Already in his first year (1921) he pro-
posed a formula for the doublet splitting
in atomic spectra and in the following
years he wrote a number of papers on
complex spectra and the vector model.
This is not the place to try to describe this
work,1 so let me say only that in 1925 Sam
was already a well known theoretical

spectroscopist. He was the “house the-
oretician” in the Zeeman laboratory in
Amsterdam, where he spent the first three
days of the week — returning to Leiden in
time for the Wednesday colloquium.
Moreover, being from the Ehrenfest
school, he was a good teacher!

So that summer Sam explained to me,
in a nice orderly fashion, the work of Al-
fred Lande, Werner Heisenberg, Pauli
and others (himself included) on the
vector model of the atom, of which I was
completely ignorant. Again I will not go
into details, so let me only remind the
reader that in this model (also sometimes
called “das Rumpf-Modell”) it was as-
sumed, say for alkali atoms, that somehow
the core ( der Rumpf ) had an angular
momentum h/ 2 and a magnetic moment
of one Bohr magneton, so that the gyro-
magnetic ratio was twice the classical
value, e/2 me, for the orbital motion of
electrons. This was a riddle, but with this
assumption one could understand very

252

HISTORY OF PHYSICS

satisfactorily the coupling of the core with
the outside electron, the influence of
magnetic field (the Lande formula), and
so on.

I remember that I was interested, but
still detached. I asked many questions,
and I made notes after each session. I
remember that I was especially bothered
by Goudsmit’s statement that the model
described all atoms except hydrogen, for
which the old Sommerfeld theory was
valid — as though that were somehow a
horse of a different color! My skepticism
infected Sam, and he then got the idea of
looking into the way the level scheme of
the fine structure of hydrogen would have
to be if it were like an alkali atom. In our
next session he already had it all worked
out. It is the now accepted level scheme
(except for the Lamb shift), which of
course also follows from the Dirac theory
of the electron. We realized that al-
though the level splittings were the same
as in the Sommerfeld theory, the selection
rules were different; the theory thus ex-
plained a mysterious strong line in the
spectrum of ionized helium that had been
observed by Friedrich Paschen. This line
was forbidden in the Sommerfeld theory
and could also not be explained by the
influence of electric fields, as I found out
from H. A. Kramers’s thesis.

It was our first success. We wrote a
paper11 in Dutch, which appeared in
Physica; although it did not attract any
attention until much later, I was quite
proud of my first contribution to physics.
However, I still had not yet completely
made up my mind to continue. There
was an opportunity for students at Leiden
who wanted to switch to the humanities
to take courses in the classical languages.
So in the beginning of September I start-
ed to take Latin. Unfortunately this
course was not like the Berlitz school in

Rome, where I had started to learn Ital-
ian! It was very tough and, after a month
or so, it became too much for me. During
this time also my sessions with Sam be-
came more and more absorbing. Ehren-
fest was away, so we talked almost every
day, trying to understand the ideas of
Pauli.

Euphoria

Sam had earlier explained to me Pauli’s
criticism against das Rumpf-Modell, and
he had told me about Pauli’s proposal to
ascribe four quantum numbers to each
electron. He now continued with the
discussion of the famous paper of January
1925 in which Pauli formulated the ex-
clusion principle: No two electrons could
have the same four quantum numbers.
He explained to me how, by combining
the four quantum numbers of the differ-
ent electrons according to the rules of the
vector model, one could understand the
periodic system and the general multiplet
structure of the atomic levels. Sam
himself had simplified the argument by
introducing the quantum numbers, n, l,
mi, and ms (appropriate when a strong
magnetic field is present) instead of those
used by Pauli, and he noticed that then
ms was always ±%.

I was impressed, but since the whole
argument was purely formal, it seemed
like abracadabra to me. There was no
picture that at least qualitatively con-
nected Pauli’s formalism with the old
Bohr atomic model. It was then that it
occurred to me that, since (as I had
learned) each quantum number corre-
sponds to a degree of freedom of the
electron, the fourth quantum number
must mean that the electron had an ad-
ditional degree of freedom — in other
words, the electron must be rotating!
Sam has written that he did not know at

that time what a degree of freedom was.
This may be so, as Sam had not done his
exam in mechanics yet; in fact, he never
passed this exam, and as a result he did
not have the right to teach mechanics in
the Dutch high schools even after he got
his PhD. However, this did not prevent
him later from teaching the graduate
course in mechanics at the University of
Michigan, which he did regularly because
he liked the subject so much; furthermore,
it was much appreciated by the students.

In spite of this he appreciated right
away that if the angular momentum of the
electron was hi 2, one had a picture of the
alkali doublets as the two ways the elec-
tron could rotate with respect to its orbital
motion. In fact, if one assumed that the
gyromagnetic ratio for the rotation was
twice the classical value, so that the
magnetic moment was

e h

2 = one Bohr magneton

2 me 2 6

then the properties formerly attributed to
the core were now properties of the elec-
tron. The simple “anschaulichen” fea-
tures of the original Rumpf-Modell were
thus reconciled with Pauli’s ideas.

I remember that when this became
clear to us, we had a feeling of euphoria,
but we also both agreed that one could not
possibly publish such stuff. Since it had
not been mentioned by any of the au-
thorities (we did not know about Kronig,
of course) it must for some reason be
nonsense. But, of course, we told
Ehrenfest, who was immediately inter-
ested. I am not sure precisely what hap-
pened next. Sam is wrong when he writes
that he was satisfied and did not think
any more about how our model could be
justified. I remember that he wrote me
a postcard from Amsterdam very soon
afterward, in which he asked whether I

UWVGM»TGT€TS IM6TITUT lUHHfrU », *.

TtoMTiM rim «... 22/12 *»5.

Lleber Ehrenfest,

Das Aufentbalt bei Itsr In Leiden war
elna wunderbare Erlebniss, lob soil dleh
tamer dankbar aeln, dass du den Anlasa war,
dass lch daa sch"6ne Jubil'ium von Lcrentz
be lwohnte. Auch die Gespr'dchen mlt Einstein
war eln grasses Genuss und Belehrung als
lch sagen kann. Nioht wenlger Freuds war ee
fUr mleh, den Elnaatz von Ullenbach und
Goudsmith kennen zu lernen. lch bln Bberzaugt,
dase es eln Bberaus grosser Fortaohrltt In
der Theorie de» Atombau bedeutet. Aaf melner
welteren Beiee fBhlte lch mlch ganz wle eln
Profet des Elektrormagnet-Evangelluos, und
loh glaube, dase es mlr gelungen 1st, Hei-

senberg und Pauli wenlgstens davon zu \iber-
zeugen, dass ihre bisherlgen EinwEnde niebt
entseheidend sind, und dees es ‘dusseret wahr-
sohelnlleh 1st, dass die quantenraeehanlsche

Durohrechnung alls Elnzelhelten rlobtlg
wiedergeben wird. Xoh frees mlch sehr daradf,
den Artlkel von Goudsmith und UUenbeoh zu
sehen. Io .Utrecht verbrachte lch olne sehr
eohtsne Abend mlt Ornatein.

Hit den beeten WOnsohen fOr einen froben
lelhnaohten und glBcfrltcbea Neujahr nir I
alle von itargrethe und

Dslnem

Bohr’s letter to
Ehrenfest. Although
he misspelled both
their names, Bohr
was enthusiastic
about the “electron-
magnet gospel” of
Uhlenbeck and
Goudsmit. He
thought it extremely
likely that the
quantum-mechanical
calculation would
reproduce all details
correctly. (From
the AIP Niels Bohr
Library.)

PERSONAL ACCOUNTS

253

was sure that the gyromagnetic ratio had
to be e/2 me classically — perhaps it was
different for the rotation of an extended
charged body. I showed this postcard to
Ehrenfest, who then recalled a paper by
Max Abraham12 about the magnetic
properties of rotating electrons. 1 studied
this paper very hard and found there to
my great satisfaction that if the electron
has only surface charge the gyromagnetic
ratio was 2 e/2mc, just as we had postu-
lated! I think that when I showed this to
Ehrenfest he thought (as he told us later)
that our idea was either very important or
nonsense, but that it should be published.
The Abraham calculations were nonre-
lativistic and based on the old-fashioned
rigid electron, so that they were at best
only suggestive. Anyway, Ehrenfest told
us to write a short, modest Letter to
Naturwissenschaften and to give it to
him. “Und dann werden wir Herrn Lo-
rentz fragen. ” (“And then we will ask Mr
Lorentz.”) A letter of 16 October to H. A.
Lorentz in which he mentions this (among
other things) was found and shown to me
by Martin Klein.

Lorentz, who was of course the great old
man of Dutch physics, was retired and
lived in Haarlem but gave a lecture in
Leiden every Monday at 11:00 am, in
which he discussed the recent develop-
ments in physics. Everybody who could
possibly make it came. So when school
started in the middle of October (re-
member, we had long vacations) I had the
opportunity to tell Lorentz about our
ideas. Sam was not present because he
had to resume his duties at the Zeeman
laboratory. Lorentz was very kind and
interested, although I also got the im-
pression that he was rather skeptical. He
said that he would think about it and that
we should talk again the next Monday.

In fact, when we met that day he
showed me a stack of papers full of cal-
culations written in his beautiful hand-
writing, which he tried to explain to me.
They were above my head but I under-
stood enough to realize that there were
serious difficulties. If the radius of the
electron was

r0 = e2/mc 2

and if it rotated with an angular momen-
tum hi 2, then the surface velocity would
be about ten times the light velocity! If
the electron had a magnetic moment
eh/2mc, its magnetic energy would have
to be so big that, to keep the mass m, its
radius would have to be at least ten times

ro-

It seemed to me that if one extended
the Abraham calculations properly as
Lorentz had apparently done, (and pub-
lished in revised form13) then our picture
of a quantized rotation of the electron
could not possibly be reconciled with
classical electrodynamics. I told this to
Ehrenfest, of course, and said that his
second alternative had turned out to be
the right one. The whole thing was non-

sense, and it would be better that our
Letter not be published. Then, to my
surprise, Ehrenfest answered that he had
already sent the Letter off quite a while
ago, and that it would appear pretty soon.
He added: “Sie sind beide jung genug
um sich eine Dummheit leisten zu kon-
nen!” (“You are both young enough to be
able to afford a stupidity!”)

This is not yet the end of the story.
Our letter appeared in the middle of No-
vember, and soon afterwards (21 No-
vember) Goudsmit received a letter from
Heisenberg, whom he knew quite well. In
this letter (reproduced in reference 2)
Heisenberg expressed his appreciation for
Sam’s courageous idea and agreed that it
would remove all of the difficulties of the
Pauli theory. He especially noted that it
leads to the Lande-Sommerfeld formula
for the alkali doublets except for a factor
of two, and he asked how we had got rid of
this factor. We had not derived this
formula and therefore had no idea about
the factor of two. In fact, I must say in
retrospect that Sam and I in our euphoria
had really not appreciated a basic diffi-
culty— one with which Pauli and Bohr
had been struggling for some time:

Clearly if one formally assigns the
Lande quantum numbers of the atomic
core to the electron as Pauli had done,
then since there is no model, it is quite
obscure how the “core” quantum number
is coupled to the orbital quantum number
of the electron. Bohr had speculated
about a new force — the “unmechanische
Zwang” (non-mechanical strain) — and
Pauli spoke about an intrinsic two-va-
luedness of the motion of the electron. In
our Letter we had maintained that such
ideas could be replaced by a hypothesis
about the structure of the electron. This
explains the rather esoteric title of our
Letter: “Replacement of the Hypothesis
of the Non-mechanical Strain by an As-
sumption about the Internal Behavior of
Every Single Electron.”

Nevertheless, we had not actually ex-
plained how the basic difficulty would
then be removed by the coupling of the
rotational and orbital motion of the elec-
tron. Now we heard from Heisenberg
that there was such a spin-orbit coupling
and that it gave the right answer except
for the mysterious factor of two. We still
did not know how to derive the formula,
but of course knowing the answer helps!
Einstein, who visited Leiden every year
for a month or so, gave us the essential
hint. In the coordinate system in which
the electron is at rest, the electric field E
of the moving atomic core produces a
magnetic field [E X v]/c (where v is the
velocity of the electron) according to the
transformation formula of relativity
theory. This sounds learned (and in those
days I liked that!), but it is of course just
the magnetic field produced by the mov-
ing charged core. It is with respect to this
magnetic field that the spin of the elec-
tron has its two orientations and the en-

ergy difference — the doublet splitting —
could then be calculated by first-order
perturbation theory. In this way we re-
produced Heisenberg’s formula with the
same erroneous factor of two. By the
way, there is no doubt that Kronig also
had done this calculation (see “The
Turning Point,” 6 page 20) and had shown
it to Lande and Pauli. I find the reaction
of Pauli mentioned there quite surprising,
and it is certainly opposite to the sympa-
thetic reaction of Ehrenfest to our ideas.
Of course one must remember that Pauli
was about of our age and was in the mid-
dle of the developments, while Ehrenfest
was twenty years older and not deeply
involved in what was sometimes called
“spectral-term zoology.”

This brings us to the beginning of De-
cember 1925 when Bohr came to Leiden
to help celebrate the fiftieth anniversary
of the doctorate of Lorentz, which was a
great occasion. Bohr’s visit was very
lucky for us, since it gave us the opportu-
nity to talk at length with him about our
idea and the subsequent difficulties.
Bohr had seen our Letter, but he still
worried about how the coupling between
the spin and the orbit could be under-
stood. When we explained Einstein’s
argument he was completely convinced
and became quite enthusiastic. He did
not pay any attention to the calculations
of Lorentz, which I mentioned to him.
“They raise just classical difficulties,” he
said, “and they will disappear when the
real quantum theory is found.” The
factor of two he took more seriously, but
he somehow expected that a better cal-
culation would also make it disappear.

He advised us to go back to the spec-
trum of hydrogen, especially when we told
him about our earlier paper in Physica,
with which he was not acquainted. Did
the combination of the Sommerfeld rel-
ativistic effect with the spin-orbit cou-
pling (forgetting about the factor of two)
lead to the fine structure of the hydrogen
levels as we had surmised in our Physica
article? Sam could show this right away,
and I think that together with the general
Lande-Pauli unification, it completely
convinced Bohr. On his way back to
Copenhagen he made propaganda for our
idea, as shown in the following part of a
letter to Ehrenfest of 22 December:

“. . . I am convinced that it implies a
large step forward for the theory of
atomic structure. On my further
travels I felt completely like a prophet
for the electron-magnet gospel, and I
believe that I have succeeded in con-
vincing Heisenberg and Pauli that at
least their present objections are not
decisive and that it is very probable
that a quantum-mechanical calcula-
tion will give all details correctly. I
am looking forward to seeing the arti-
cle of Goudsmit and Uhlenbeck . . .”
This article was our second Letter to the
Editor, this time that of Nature. 14 P was
entitled: “Spinning Electrons and the

254

HISTORY OF PHYSICS

Structure of Spectra.” It was dated De-
cember 1925 and appeared 20 February
1926. Bohr added an approving post-
script. Since then our idea has been more
or less accepted. The only holdout was
Pauli, who had not been convinced by
Bohr and who still spoke of it as the new
“brlehre” (“erroneous teachings”) (see
van der Waerden’s article, reference 7,
page 215).

And there was of course still the mys-
terious factor of two! It is now well
known that this difficulty was soon af-
terwards resolved15 by L. H. Thomas, who
showed that it was a forgotten relativistic
effect. I remember that, when I first
heard about it, it seemed unbelievable
that a relativistic effect could give a factor
of two instead of something of order v/c.

I will not try to explain it, so let me only
say that even the cognoscenti of the rela-
tivity theory (Einstein included!) were
quite surprised. When Pauli understood
it he finally withdrew his objections, as he
mentioned later in his Nobel Prize lec-
ture.16

This is the end of the story so far as
Sam and I are concerned. I had become
the assistant of Ehrenfest and in 1926 we
worked together trying to digest the new
quantum mechanics, and especially to
understand the consequences for statis-
tical mechanics. Sam continued his
spectroscopic work, partially in Tubingen,
where together with Ernst Back he
worked out the theory of the hyperfine
structure of the spectral lines when the
atomic nucleus has a spin and magnetic
moment. 17 In the spring of 1927 we both
spent a few months in Copenhagen, where
we wrote our dissertations. We received
our doctor’s degrees on the same day (7
July 1927) and then in the fall we went on
the same boat to the US and to Ann
Arbor, Michigan, where we had been ap-
pointed as instructors of physics.

With regard to the spin of the electron,
it was of course Pauli who succeeded in
incorporating the notion into Schrodinger
wave mechanics.18 It must have been a
great satisfaction for him that it required
a two-valued, or spinor, wave function.
In a way it justified his old speculation on
the two-valuedness of the electron mo-
tion. In his paper Pauli still had to as-
sume the anomalous factor of two for the
gyromagnetic ratio and he also had to take
over the Thomas factor of two. The
really complete explanation of these two
factors of two, which had plagued the
theory, did not come until 1928, when
Paul Dirac developed the complete rela-
tivistic wave equation of the electron.19

* * *

lam indebted to Martin Klein for a copy of the
letter from Rohr to Ehrenfest; the translation
from the German is mine.

This article is an adaptation of a talk pre-
sented 2 February at the joint New York
meeting of The American Physical Society
and the American Association of Physics

Teachers as part of a symposium celebrating
the 50th anniversary of the discovery of elec-
tron spin.

References

1. S. A. Goudsmit, “The discovery of the
electron spin,” lecture given on the ac-
ceptance of the Max-Planck medal, in
Proceedings of the Physikertagung,
Frankfurt (1965); a German translation
appeared in Physikalische Blatter, Heft
9/10 (1965).

2. S. A. Goudsmit, talk given at the 50th an-
niversary of the Dutch Physical Society in
April 1971, Ned. Tydschrift voor Natuur-
kunde 37, 386 (1971); in Dutch.

3. S. A. Goudsmit, Delta 15, 77 (1972); ex-
cerpts from reference 2, in English.

4. G. Uhlenbeck, Oude en Nieuwe Vragen
der Natuurkunde, North-Holland, Am-
sterdam (1955); partial English translation
by B. L. van der Waerden, in Theoretical
Physics in the Twentieth Century, Inter-
science, New York (1960).

5. E. H. Kennard, Phys. Rev. (2nd series) 19,
420(1922).

6. R. Kronig, “The Turning Point,” in The-
oretical Physics in the Twentieth Century,
Interscience, New York (1960).

7. B. L. van der Waerden, “Exclusion Prin-
ciple and Spin,” in Theoretical Physics in
the Twentieth Century, Interscience, New
York (1960).

8. G. E. Uhlenbeck, “Reminiscences of Pro-
fessor Paul Ehrenfest,” Amer. J. Phys. 24,
431 (1956).

9. G. E. Uhlenbeck, “Over Johannes Heck-
ius,” Comm, of the Dutch Historical In-
stitute in Rome 4, 217 (1924).

10. Collected Papers of P. Ehrenfest, North-
Holland, Amsterdam, page 526 (1959).

11. S. A. Goudsmit, G. E. Uhlenbeck, Physica
5, 266(1925).

12. M. Abraham, Ann. der Physik 10, 105
(1903).

13. H. A. Lorentz, Collected Works, Martinus
Nyhoff, The Hague ( 1934), volume 7, page
179.

14. G. E. Uhlenbeck, S. A. Goudsmit, Nature
117,264 (1926).

15. L. H. Thomas, Nature 117, 514 (1926).

16. W. Pauli, Collected Scientific Papers,
volume 2, page 1080.

17. S. A. Goudsmit, PHYSICS TODAY, June
1961, page 18.

18. W. Pauli, Z. Physik 43, 601 (1927).

19. P. A. M. Dirac, Proc. Roy. Soc. A 1 17, 610

(1928); A 118, 351 (1928); one should also
not forget the contributions of H. A. Kra-
mers: Quantentheorie des Elektrons und
der Strahlung, in Hand- und Jahrbuch der
Chemischen Physik, Akad. Verlagsges.,
Leipzig (1937); English translation,
Quantum Mechanics, by D. ter Haar,
North-Holland, Amsterdam (1957). □

Bosscha Reading Room, the physics and mathematics library at the University of Leiden. Students
without a classical education, such as George Uhlenbeck, were barred from Leiden before 1919.

PERSONAL ACCOUNTS

255

PART I PHYSICS TODAY / OCTOBER 1959

History of the CYCLOTRON

On May 1, 1959, in memory of the late Ernest Orlando Lawrence,
two invited lectures on the history of the cyclotron were presented as
part of the American Physical Society’s annual spring meeting in
Washington, D. C. The present article is based on Prof. Livingston’s
talk on that occasion. The second speaker was E. M. McMillan, whose
illustrated account also appears in this issue beginning on p. 24.

By M. Stanley Livingston

THE principle of the magnetic resonance accel-
erator, now known as the cyclotron, was proposed
by Professor Ernest 0. Lawrence of the Univer-
sity of California in 1930, in a short article in Science
by Lawrence and N. E. Edlefsen.1 It was suggested by
the experiment of Wideroe 2 in 1928, in which ions of
Na and K were accelerated to twice the applied voltage
while traversing two tubular electrodes in line between
which an oscillatory electric field was applied — an ele-
mentary linear accelerator. In 1953 Professor Lawrence
described to the writer the origin of the idea, as he
then remembered it.

The conception of the idea occurred in the library
of the University of California in the early summer
of 1929, when Lawrence was browsing through the
current journals and read Wideroe’s paper in the Archiv
fur Elektrotechnik. Lawrence speculated on possible
variations of this resonance principle, including the use
of a magnetic field to deflect particles in circular paths
so they would return to the first electrode, and thus
reuse the electric field in the gap. He discovered that
the equations of motion predicted a constant period of
revolution, so that particles could be accelerated in-
definitely in resonance with an oscillatory electric field
— the “cyclotron resonance” principle.

Lawrence seems to have discussed the idea with
others during this early formative period. For example,
Thomas H. Johnson has told the writer that Lawrence
discussed it with himself and Jesse W. Beams during
a conference at the Bartol Institute in Philadelphia
during that summer, and that further details grew out
of the discussion.

The first opportunity to test the idea came during
the spring of 1930, when Lawrence asked Edlefsen,
then a graduate student at Berkeley who had completed

his thesis and was awaiting the June degree date, to
set up an experimental system. Edlefsen used an existing
small magnet in the laboratory and built a glass vacuum
chamber with two hollow internal electrodes to which
radiofrequency voltage could be applied, with an un-
shielded probe electrode at the periphery. The current
to the probe varied with magnetic field, and a broad
resonance peak was observed which was interpreted
as due to the resonant acceleration of hydrogen ions.

However, Lawrence and Edlefsen had not in fact
observed true cyclotron resonance; this came a little
later. Nevertheless, this first paper was the initial
announcement of a principle of acceleration which was
soon found to be valid and which became the basis for
all future cyclotron development.

M. Stanley Livingston, professor of physics at the Massachusetts
Institute of Technology, is director of the Cambridge Electron Ac-
celerator project at Harvard University, a program conducted under
the joint auspices of Harvard and MIT.

Fig. 1. Vacuum chamber of the first cy-
clotron. (PhD Thesis, M. S. Livingston,
University of California, April 14, 1931)

256

HISTORY OF PHYSICS

Doctoral Thesis

TN the summer of 1930 Professor Lawrence suggested
-*■ the problem of resonance acceleration to the author,
then a graduate student at Berkeley, as an experimental
research investigation. In my early efforts to confirm
Edlefsen’s results I found that the broad peak ob-
served by him was probably due to single acceleration
of N and 0 ions from the residual gas, which curved
in the magnetic field and struck the unshielded electrode
at the edge of the chamber.

It was my opportunity and responsibility to continue
the study and to demonstrate true cyclotron resonance.
A Doctoral Thesis 3 by the author dated April 14, 1931,
reported the results of the study. It was not published
but is on file at the University of California library.
The electromagnet available was of 4-inch pole diameter.
Fig. 1 is an illustration from this thesis, showing the
arrangement of components which is still a basic fea-
ture of all cyclotrons. The vacuum chamber was made
of brass and copper. Only one “D” w'as used, on this
and several subsequent models; the need for a more
efficient electrical circuit for the radiofrequency elec-
trodes came later with the effort to increase energy.
A vacuum tube oscillator provided up to 1000 volts on
the electrode, at a frequency which could be varied
by adjusting the number of turns in a resonant in-
ductance. Hydrogen ions (H2+ and later H+) were
produced through ionization of hydrogen gas in the
chamber, by electrons emitted from a tungsten-wire
cathode at the center. Resonant ions which reached
the edge of the chamber were observed in a shielded
collector cup and had to traverse a deflecting electric
field. Sharp peaks were observed in the collected cur-
rent at the magnetic field for resonance with H2+ ions
as shown in Fig. 2, a typical resonance curve taken
from the thesis. Also present were 3/2 and S/2 reso-
nance peaks at proportionately lower magnetic fields,

due to harmonic resonances of H2* ions. By varying
the frequency of the applied electric field, resonance
was observed over a wide range of frequency and
magnetic field, as shown in Fig. 3, proving conclusively
the validity of the resonance principle.

The small magnet used in these resonance studies
had a maximum field of 5200 gauss, for which reso-
nance with Ho* ions occurred at 76 meters wavelength
or 4.0 megacycles frequency. In this small chamber the
final ion energy was 13 000 electron volts, obtained with
the application of a minimum of 160 volts peak on
the D. This corresponds to about 40 turns or 80 accel-
erations. A stronger magnet was borrowed for a short
time, capable of producing 13 000 gauss, with which
it was possible to extend the resonance curve and to
produce hydrogen ions of 80 000 ev energy. This goal
w'as reached on January 2, 1931.

The First 1-Mev Cyclotron

1AWRENCE moved promptly to exploit this break-
J through. In the spring of 1931 he applied for and
was awarded a grant by the National Research Council
(about $1000) for a machine w’hich could give useful
energies for nuclear research. The writer was appointed
as an instructor at the University of California on
completion of the doctorate in order to continue the
research. During the summer and fall of 1931, the
writer, under the supervision of Lawrence, designed and
built a 9-inch diameter magnet and brought it into
operation, first with H2+ ions of 0.5-Mev energy. Then
the poles were enlarged to 11 inches and protons were
accelerated to 1.2 Mev. This was the first time in scien-
tific history that artificially accelerated ions of this
energy had been produced. The beam intensity avail-
able at a target was about 0.01 microampere. The
progress and results w'ere reported in a series of three

Fig. 2. Typical curves of current at the collector vs. magnetic field, Fig. 3. Experimental values

showing resonant H2+ ions of 13 000 ev energy (peak D) and the of cyclotron resonance for

variation of intensity with hydrogen gas pressure. (Thesis — Livingston) H2* ions. (Thesis — Livingston)

PERSONAL ACCOUNTS

257

Fig. 4. 1.2 Mev H+ cyclotron
at the University of California.4

Fig. 5. Vacuum chamber for 1.2 Mev
cyclotron with 11-inch pole faces.4

abstracts and papers by Lawrence and Livingston in
The Physical Review. 4 Figs. 4 and 5 show the size and
general arrangements of this first practical cyclotron.

Of course, Lawrence had other interests and other
students in the laboratory. Milton White continued
research with the first cyclotron. David Sloan developed
a series of linear accelerators for heavy ions, limited
by the radio power tubes and techniques available at
that time, for Hg ions and later for Li ions. With
Wesley Coates, Robert Thornton, and Bernard Kinsey,
Sloan also invented and developed a resonance trans-
former using a radiofrequency coil in a vacuum cham-
ber which developed 1 million volts. With Jack Livin-
good and Frank Exner he tried for a time to make
this into an electron accelerator. I must again thank
Dave Sloan for the many times that he assisted me
in solving problems of the cyclotron oscillator.

The Race for High Voltage

TO understand the meaning of this achievement we
must look at it from the perspective of the status
of science throughout the world. When Rutherford
demonstrated in 1919 that the nitrogen nucleus could
be disintegrated by the naturally occurring alpha par-
ticles from radium and thorium, a new era was opened
in physics. For the first time man was able to modify
the structure of the atomic nucleus, but in submicro-
scopic quantities and only by borrowing the enormous
energies (S to 8 Mev) of radioactive matter. During
the 1920’s x-ray techniques were developed so ma-
chines could be built for 100 to 200 kilovolts. Develop-
ment to still higher voltages was limited by corona
discharge and insulation breakdown, and the multi-
million volt range seemed out of reach.

Physicists recognized the potential value of artificial
sources of accelerated particles. In a speech before the
Royal Society in 1927 Rutherford expressed his hope
that accelerators of sufficient energy to disintegrate
nuclei could be built. Then in 1928 Gamow and also

Condon and Gurney showed how the new wave me-
chanics, which was to be so successful in atomic science,
could be used to describe the penetration of nuclear
potential barriers by charged particles. Their theories
made it seem probable that energies of S00 kilovolts
or less would be sufficient to cause the disintegration
of light nuclei. This more modest goal seemed feasible.
Experimentation started around 1929 in several labora-
tories to develop the necessary accelerating devices.

This race for high voltage started on several fronts.
Cockcroft and Walton in the Cavendish Laboratory of
Cambridge University, urged on by Rutherford, chose
to extend the known engineering techniques of the
voltage-multiplier, which had already been successful
in some x-ray installations. Van de Graaff chose the
long-known phenomena of electrostatics and developed
a new type of belt-charged static generator to obtain
high voltages. Others explored the Tesla coil trans-
former with an oil-insulated high-voltage coil, or the
“surge-generator” in which capacitors are charged in
parallel and discharged in series, and still others used
transformers stacked in cascade on insulated platforms.

The first to succeed were Cockcroft and Walton.5
They reported the disintegration of lithium by protons
of about 400 kilovolts energy, in 1932. I like to con-
sider this as the first significant date in accelerator
history and the practical start of experimental nuclear
physics.

All the schemes and techniques described above have
the same basic limitation in energy; the breakdown of
dielectrics or gases sets a practical limit to the voltages
■which can be successfully used. This limit has been
raised by improved technology, especially in the pres-
sure-insulated electrostatic generator, but it still re-
mains as a technological limit. The cyclotron avoids this
voltage-breakdown limitation by the principle of reso-
nance acceleration. It provides a method of obtaining
high particle energies without the use of high voltage.

258

HISTORY OF PHYSICS

The Cyclotron Splits its First Atoms

THE above digression into the story of the state
of the art shows why the 1.2-Mev protons from
the 11-inch Berkeley cyclotron were so important.
This small and relatively inexpensive machine could
split atoms! This was Lawrence’s goal. This was why
Lawrence literally danced with glee when, watching over
my shoulder as I tuned the magnet through resonance,
the galvanometer spot swung across the scale indicating
that 1 000 000-volt ions were reaching the collector.
The story quickly spread around the laboratory and we
were busy all that day demonstrating million-volt pro-
tons to eager viewers.

We had barely confirmed our results and I was busy
with revisions to increase beam intensity when we re-
ceived the issue of the Proceedings of the Royal
Society describing the results of Cockcroft and Walton
in disintegrating lithium with protons of only 400 000
electron volts. We were unprepared at that time to
observe disintegrations with adequate instruments. Law-
rence sent an emergency call to his friend and former
colleague, Donald Cooksey at Yale, who came out to
Berkeley for the summer with Franz Kurie; they helped
develop the necessary counters and instruments for
disintegration measurements. Within a few months after
hearing the news from Cambridge we were ready to
try for ourselves. Targets of various elements were
mounted on removable stems which could be swung
into the beam of ions. The counters clicked, and we
were observing disintegrations! These first early results
were published on October 1, 1932, as confirmation of
the work of Cockcroft and Walton, by Lawrence,
Livingston, and White.6

The “ 27-inch ” Cyclotron

LONG before I had completed the 11-inch machine
V as a working accelerator, Lawrence was planning
the next step. His aims were ambitious, but supporting

funds were small and slow in arriving. He was forced
to use many economies and substitutes to reach his
goals. He located a magnet core from an obsolete
Poulsen arc magnet with a 45-inch core, which was
donated by the Federal Telegraph Company. Two pole
cores were used and machined to form the symmetrical,
flat pole faces for a cyclotron. In the initial arrange-
ment the pole faces were tapered to a 27T2-inch
diameter pole face; in later years this was expanded to
34 inches and still higher energies were obtained. The
windings were layer-wound of strip copper and im-
mersed in oil tanks for cooling. (The oil tanks leaked!
We all wore paper hats when working between coils
to keep oil out of our hair.) The magnet was installed
in the “old radiation lab” in December 1931; this was
an old frame warehouse building near the University
of California Physics Building which was for years the
center of cyclotron and other accelerator activities.
Fig. 6 is a photograph of this magnet with the vacuum
chamber rolled out for modifications.

Other dodges were necessary to meet the mounting
bills for materials and parts. The Physics Department
shops were kept filled with orders for machining. Will-
ing graduate students worked with the mechanics in-
stalling the components. My appointment as instructor
terminated, and for the following year Lawrence ar-
ranged for me an appointment as research assistant in
which I not only continued development on the cyclo-
tron but also supervised the design and installation of
a 1-Mev resonance transformer x-ray installation of the
Sloan design in the University Hospital in San
Francisco.

The vacuum chamber for the 27-inch machine was
a brass ring with many radial spouts, fitted with “lids”
of iron plate on top and bottom which were extensions
of the pole faces. This chamber is shown in Fig. 7.
Sealing wax and a special soft mixture of beeswax and
rosin were first used for vacuum seals, but were ulti-
mately replaced by gasket seals. In the initial model

PERSONAL ACCOUNTS

only one insulated D-shaped electrode was used, facing
a slotted bar at ground potential which was called a
“dummy D”. In the space behind the bar the collector
could be mounted at any chosen radius. The beam
was first observed at a small radius, and the magnet
was “shimmed” and other adjustments made to give
maximum beam intensity. Then the chamber was
opened, the collector moved to a larger radius, and
the tuning and shimming extended. Thus we learned,
the hard way, of the necessity of a radially decreasing
magnetic field for focusing. If our optimism persuaded
us to install the collector at too large a radius, we
made a “strategic retreat” to a smaller radius and re-
covered the beam. Eventually we reached a practical
maximum radius of 10 inches and installed two sym-
metrical D’s with which higher energies could be at-
tained. Technical improvements and new gadgets were
added day by day as we gained experience. The prog-
ress during this period of development from 1-Mev
protons to 5-Mev deuterons was reported in The Physi-
cal Review by Livingston 1 in 1932 and by Lawrence
and Livingston 8 in 1934.

I am indebted to Edwin M. McMillan for a brief
chronological account of these early developments on
the 27-inch cyclotron. (It seems that earlier laboratory
notebooks were lost.) These records show, for example:

June 13, 1932. 16-cm radius, 28-meter wavelength, beam
of 1.24-Mev H2+ ions.

August 20, 1932. 18-cm radius, 29 meters, 1.58-Mev
HT ions.

August 24, 1932. Sylphon bellows put on filament for
adjustment.

September 28, 1932. 25.4-cm radius, 25.8 meters, 2.6-
Mev H2+ ions.

October 20, 1932. Installed two D’s in tank, radius fixed
at 10 in.

November 16, 1932. 4.8-Mev H»+ ions, ion current 1CTB
amps.

December 2-5, 1932. Installed target chamber for stud-
ies of disintegrations with Geiger counter. Start of
long series of experiments.

March 20, 1933. 5 Mev of H2+; 1.5 Mev of He+; 2
Mev of (HD)+. Deuterium ions acelerated for first
time.

September 27, 1933. Observed neutrons from targets
bombarded by D+.

December 3, 1933. Automatic magnet current control
circuit installed.

February 24, 1934. Observed induced radioactivity in C
by deuteron bombardment. 3-Mev D+ ions, beam
current 0.1 microampere.

March 16, 1934. 1.6-Mev H+ ions, beam current 0.8
microampere.

April-May, 1934. 5.0-Mev D+ ions, beam current 0.3
microampere.

Those were busy and exciting times. Other young
scientists joined the group, some to assist in the con-
tinuing development of the cyclotron and others to
develop the instruments for research instrumentation.
Malcolm Henderson came in 1933 and developed count-
ing instruments and magnet control circuits, and also

spent long hours repairing leaks and helping with the
development of the cyclotron. Franz Kurie joined the
team, and Jack Livingood and Dave Sloan continued
with their linear accelerators and resonance transform-
ers, but were always available to help with problems
on the cyclotron. Edwin McMillan was a major thinker
in the planning and design of research experiments. And
we all had a fond regard for Commander Telesio Lucci,
retired from the Italian Navy, who became our self-
appointed laboratory assistant. As the experiments
began to show results we depended heavily on Robert
Oppenheimer for discussions and theoretical interpre-
tation.

One of the exciting periods was our first use of
deuterons in the cyclotron. Professor G. N. Lewis of
the Chemistry Department had succeeded in concen-
trating “heavy water” with about 20% deuterium from
battery acid residues, and we electrolyzed it to obtain
gas for our ion source. Soon after we tuned in the first
beam we observed alpha particles from a Li target with
longer range and higher energy than any previously
found in natural radioactivities — 14.5-cm range, coming
from the Li6 (d,p) reaction. These results were re-
ported in 1933 by Lewis, Livingston, and Lawrence,9
and led to an extensive program of research in deuteron
reactions. Neutrons were also observed, in much higher
intensities when deuterons were used as bombarding
particles, and were put to use in a variety of ways.

We had frustrations — repairing vacuum leaks in the
wax seals of the chamber or “tank” was a continuing
problem. The ion source filament was another weak
point, and required continuous development. And some-
times Lawrence could be very enthusiastic. I recall
working till midnight one night to replace a filament
and to reseal the tank. The next morning I cautiously
warmed up and tuned the cyclotron to a new beam
intensity record. Lawrence was so pleased and excited
when he came into the laboratory that morning that
he jubilantly ran the filament current higher and higher,
exclaiming each time at the new high beam intensity,
until he pushed too high and burned out the filament !

We made mistakes too, due to inexperience in re-
search and the general feeling of urgency in the labora-
tory. The neutron had been identified by Chadwick
in 1932. By 1933 we were producing and observing
neutrons from every target bombarded by deuterons.10
They showed a striking similarity in energy, independ-
ent of the target, and each target also gave a proton
group of constant energy. This led to the now for-
gotten mistake in which the neutron mass was calcu-
lated on the assumption that the deuteron was breaking
up into a proton and a neutron in the nuclear field.
The neutron mass was computed from the energy of
the common proton group,11 and was much lower
than the value determined by Chadwick. Shortly after-
ward, Tuve, Hafstad, and Dahl in Washington, D. C.,
using the first electrostatic generator to be completed
and used for research, showed that these protons and
neutrons came from the D (d,p) and D(d,w) reactions,

260

HISTORY OF PHYSICS

in which the target was deuterium gas deposited in all
targets by the beam. We were chagrined, and vowed
to be more careful in the future.

We also had many successful and exciting moments.
I recall the day early in 1934 (February 24) when
Lawrence came racing into the lab waving a copy of
the Comptes Rendus and excitedly told us of the dis-
covery of induced radioactivity by Curie and Joliot in
Paris, using natural alpha particles on boron and other
light elements. They predicted that the same activities
could be produced by deuterons on other targets, such
as carbon. Now it just so happened that we had a
wheel of targets inside the cyclotron which could be
turned into the beam by a greased joint, and a thin
mica window on a re-entrant seal through which we
had been observing the long-range alpha particles from
deuteron bombardment. We also had a Geiger point
counter and counting circuits at hand. We had been
making 1 -minute runs on alpha particles, with the
counter switch connected to one terminal of a double-
pole knife-switch used to turn the oscillator on and
off. We quickly disconnected this counter switch, turned

the target wheel to carbon, adjusted the counter cir-
cuits, and then bombarded the target for S minutes.
When the oscillator switch was opened this time, the
counter was turned on, and click-click-click— click- —
click. We were observing induced radioactivity within
less than a half-hour after hearing of the Curie-Joliot
results. This result was first reported by Henderson,
Livingston, and Lawrence 12 in March. 1934.

I left the laboratory in July, 1934, to go to Cornell
(and later to MIT) as the first missionary from the
Lawrence cyclotron group. Edwin McMillan overlapped
my term of apprenticeship by a few months, and
stayed on to win the Nobel Prize and ultimately to
succeed Professor Lawrence as director of the labora-
tory which he founded. McMillan can tell the rest
of the story.

But it would be unfair to the spirit of Professor
Lawrence if I failed to indicate some gleam of great
things to come, some vision of the future. Recently
I prepared a graph of the growth of particle energies
obtained with accelerators with time, shown in Fig. 8.
To keep this rapidly rising curve on the plot, the
energies are plotted on a logarithmic scale. The curves
show the growth of accelerator energy for each type
of accelerator plotted at the dates when new voltage
records were achieved. The cyclotron was the first
resonance accelerator to be successful, and it led to
the much more sophisticated synchronous accelerators
which are still in the process of growth. The over-all
envelope to the curve of log E vs time is almost
linear, which means an exponential rise in energy, with
a 10-fold increase occurring every 6 years and with a
total increase in particle energy of over 10 000 since
the days of the first practical accelerators. The end is
not yet in sight. If you are tempted to extrapolate this
curve to 1960, or even to 1970, then you are truly
sensing the exponentially rising spirit of the Berkeley
Radiation Laboratory in those early days, stimulated
by our unique leader, Professor Lawrence.

References

1. E. O. Lawrence and N. E. Edlefsen, Science 72, 376 (1930).

2. R. Wideroe, Arch. Elektrotech. 21, 387 (1928).

3. M. S. Livingston, “The Production of High-Velocity Hydrogen
Ions without the Use of High Voltages”. PhD thesis, University of
California, April 14, 1931.

4. E. O. Lawrence and M. S. Livingston, Phys. Rev. 37, 1707 ( 193 1 ) *
Phys. Rev. 38. 136 (1931); Phys. Rev. 40, 19 (1932).

5. Sir John Cockcroft and E. T. S. Walton, Proc. Roy. Soc. 136A,
619 (1932); Proc. Roy. Soc. 137A, 229 (1932).

6. E. O. Lawrence, M. S. Livingston, and M. G. White, Phys. Rev.
42, ISO (1932).

7. M. S. Livingston, Phys. Rev. 42, 441 (1932).

8. E. O. Lawrence and M. S. Livingston, Phys. Rev. 45, 608 (1934)

9. G. N. Lewis, M. S. Livingston, and E. 0. Lawrence, Phys. Rev.
44, 55 (1933); E. O. Lawrence, M. S. Livingston, and G. N.
Lewis, Phys. Rev. 44, 56 (1933).

10. M. S. Livingston, M. C. Henderson, and E. O. Lawrence, Phys.
Rev. 44, 782 (1933); E. O. Lawrence and M. S. Livingston, Phys.
Rev. 45, 220 (1934).

11. M. S. Livingston, M. C. Henderson, and E. O. Lawrence, Phys.

Rev. 44, 781 (1933); G. N. Lewis, M. S. Livingston, M. C.

Henderson, and E. O. Lawrence, Phys. Rev. 45, 242 (1934); Phys.
Rev. 45, 497 (1934); M. C. Henderson, M. S. Livingston, and

E. O. Lawrence, Phys. Rev. 46, 38 (1934).

12. M. C. Henderson, M. S. Livingston, and E. 0. Lawrence, Phys.

Rev. 45, 428 (1934); M. S. Livingston and E. M. McMillan,

Phys. Rev. 46, 437 (1934); M. S. Livingston, M. C. Henderson,
and E. 0. Lawrence, Proc. Natl. Acad. Sci. US 20, 470 (1934);
E. M. McMillan and M. S. Livingston, Phys. Rev. 47, 452 (1935).

PERSONAL ACCOUNTS

261

PART II

PHYSICS TODAY / OCTOBER 1959

History of the CYCLOTRON

By Edwin M. McMillan

AS Dr. Livingston has told you, our activities over-
r\ lapped by a few months, so that between us
we can give a continuous story of cyclotron
development as carried out at Berkeley under the
guidance of Professor Lawrence. My start in his labo-
ratory was in April of 1934, but I was around Berkeley
before that working in Le Conte Hall on a molecular
beam problem. Therefore, I have two kinds of early
memories of the Radiation Laboratory at that time.
One is as a place that I visited occasionally before I
was working there ; the other is as a place where I came
to work, which I remember better, although it still
seems like a very long time ago. The whole way of
working was rather different from what it is in most

Nobel Laureate Edwin M. McMillan is director of the Lawrence
Radiation Laboratory at the University of California at Berkeley,
having succeeded to that post following the death of the Laboratory’s
original director, E. O. Lawrence, in 1958. The article is based on
the second of two talks presented before the American Physical Society
last May in memory of Prof. Lawrence.

laboratories today. We did practically everything our-
selves. We had no professional engineers, so we had
to design our own apparatus; we made sketches for the
shop, and did much of our own machine work; we took
all of our own data, did all our own calculations, and
wrote all our own papers. Things are now quite different
from that, because everybody does just his share and
the operations have become much larger and more pro-
fessional. While the modern method produces more
results, perhaps this older way may have been more fun.

What I have done in preparing a paper to give here
is to let it be based mainly on a set of lantern slides,
because I think pictures are more interesting than
words. I would like to run through these pictures and
try to recall what they illustrate and the various inci-
dents, some amusing, some otherwise, that go along
with them.

I’m going to start with another picture of the 27"
cyclotron. This shows the machine as it looked in 1934

HISTORY OF PHYSICS

Slide 2

when Stan and I were both there. (Slide 1.) Dr. Liv-
ingston is in the picture, and Professor Lawrence. The
machine is the same as in the views shown by Stan,
but here it is all assembled with the 27" chamber in
place. I have another view here of Professor Lawrence
sitting at the control table, showing how one operated
the machine. (Slide 2.) This was the major tool of
nuclear research of that day and this was the control
station. The switchboard in back had to do with mag-
net control, and the beam current was observed on the
galvanometer scale.

As an illustration of the kind of experimental equip-
ment one used, I have this drawing which was taken
from a publication of about that period, early in 1935.
(Slide 3.) This was an experiment to disintegrate alu-
minum with deuterons. You’ll notice that in those days
they were called deutons. The story was told that
Ernest Rutherford objected to the name deuton; he
didn’t like the sound of it, but agreed that it would
be all right if we put in his initials, E.R. (I don’t think
this story is really true, but at least the fact that it
was told is true.) Well, these deutons came along inside
the cyclotron vacuum chamber. This box is a cylinder
soldered into the side of the brass wall of the cyclotron
chamber. The beam that’s inside passes through a thin
target of aluminum foil. The secondary particles stud-
ied in this case were protons, making this an example
of a ( d,p ) reaction. We didn’t have that notation then,
but that is what it would be called now. The secondary
protons came out through a mica window, real old-
fashioned mica, and into an ionization chamber counter
and were counted. We measured the energy of these
protons by simply sliding this counter back and forth
inside of the tube, varying the range. We were measur-
ing the range in air and plotting range curves in the

way that one did in those days. This was considered
a piece of research in physics; this was published, but
nowadays, of course, nobody would think of doing a
thing quite that way.

Now, let us go on to the development of the cyclo-
tron itself. The two principal parameters of the cy-
clotron, as far as its use is concerned, are the energy
of the particles and the intensity. With that older
vacuum tank that we saw, the one that was in place

TAROET

Slide 3: Arrangement of target, screens,
and counter for bombarding in vacuum.

PERSONAL ACCOUNTS

263

Slide 4

in Slide 1, the energy was up to about 3 Mev (this is
the energy for deuterons). In 1936 a new chamber was
built which is shown in the next slide. (Slide 4.) Com-
paring it with the chamber that Livingston showed,
you’ll see that there are many changes. For instance,
the insulators for the two dees are made of Pyrex,
with flanged ends which are clamped and bolted to-
gether rather than being waxed together, as the older
ones were. The whole structure is more rugged, but
there are still old-fashioned touches. You’ll notice,
coming into the center, a filament-type ion source that
was still used then. Over in one corner you can see
a glass liquid air trap, which was a very fragile and
troublesome thing. People were always bumping into
it and, of course, when it was bumped into, we’d have
to pull the tank out, clean out the broken glass, and
put the tank together all over again. With this new
tank in place giving higher energies, up to 6 Mev for
deuterons, and also larger currents, new types of
experiments could be tried.

It was at about this time that an interest in biologi-
cal work started in the laboratory, which has continued
to the present. This was really started by John Law-
rence, Ernest Lawrence’s brother, who came out to the
laboratory in 1935 to see what we were doing, and to
see if there were any interest in the medical side. At
this time biological experiments were started. I can
recall the first time that a mouse was irradiated with
neutrons. We put the mouse in a little cage and stuck
him up on the side of the cyclotron tank and left him
there for a while. Of course, nothing happened because
there was not enough intensity. Then a serious attempt
was made to see what neutrons did to mice. The first
time this was done, it was done with an arrangement
designed by Paul Aebersold in which the mouse could
be put into the re-entrant tube shown in Slide 3, which
was built into the cyclotron tank wall. In this way he
could be close enough to the target to get some inten-
sity. This mouse came out dead. This created a great
impression at the time and I think perhaps was one
reason why, in the Lawrence Radiation Laboratory,

people have always been careful with radiation even
though it was soon discovered that somebody had for-
gotten to turn on the air supply which was supposed
to provide ventilation for this mouse so that he died
of anoxia. Anyhow, it was a very dramatic thing at
the time.

Also at about this same time the first radioactive
tracer experiments on human beings were tried. The
first one that I recall, and I think the first use any-
where of an artificially produced radioisotope in human
beings, was an early experiment of Joseph Hamilton in
which he measured the circulation time of the blood
by a very primitive method. The experimental subject
takes some radioactive sodium dissolved in water in
the form of sodium chloride, drinks it, and then has
a Geiger counter which he holds in his hand, so that
when the radioactive sodium reaches the hand, it starts
to register. His hand is in a lead box so that the stuff
that’s just in his body doesn’t affect the counter by
gamma rays. I brought along a picture of this setup.
(Slide 5.) This drawing, I believe, was made by Dr.
Hamilton’s wife, who is an artist. It shows the hand
in the box, you see this cutaway lead box, holding a
Geiger counter; the beaker with the radio sodium isn’t
shown but you might have shown him in the act of
drinking it. After he does this, within just a few sec-
onds, you begin to get some registration. After a few
minutes, you begin to get equilibrium, and from these
observations you get the circulation time of the blood.
This, of course, is a very simple beginning, just like
the simple beginning in physics that I showed with the
primitive experiment of a ( d,p ) reaction. There were
also simple beginnings of therapeutic use, coming a little
bit later, in which neutron radiation was used, for in-
stance, in the treatment of cancer. These things have
gone on and built up so that there’s now a whole field
of radio medicine which had its beginning back in
that time.

Another highlight from 1936 was the first time that
anyone tried to make artificially a naturally occurring
radionuclide (of course, we didn’t have the word nuclide

Slide 5

264

HISTORY OF PHYSICS

Slide 6

then, but that is what it would now be called). This,
I think, was a fairly classical experiment because there
were then some people who didn’t quite believe that
the artificial radioactive materials were on the same
status as the naturally occurring ones. Jack Livingood
put some bismuth in the deuteron beam of the cyclo-
tron, with an energy of about 6 Mev. This is high
enough that one does get an appreciable yield of the
( d,p ) reaction forming radium E, a bismuth isotope,
which then decays into polonium. The periods and en-
ergies were identical to those of natural radium E and
polonium, so everybody was happy. This was the first
time that one had gotten up that far in the periodic
table with a charged-particle disintegration experiment.

Another thing that we were trying to do then was
to bring the beam out of the tank. It seemed that there
might some day be a use for a beam extractor. And so
these experiments, which were spoken of as snouting
experiments — getting the beam out of a snout — were
done. Of course, in that re-entrant tube I showed
you in Slide 3 you could get the beam in air by putting
a little window on one side and letting the beam travel
about two inches across the diameter of that brass tube.
It was in air but it wasn’t really outside the tank,
because it plunged back into the wall of the tube. To
get the beam the rest of the way out, we had to in-
crease the strength of the deflecting field and move the
deflector plate out some, so as to get enough radial
displacement that the beam would come out to the
edge of the magnetic field. The next slide I’m going
to show is the first time that a beam was brought out-
side the tank in this sense. I remember this occasion
very well because when we first tried, the beam didn’t

quite clear the edge of the tank; it was coming almost
tangentially and the thickness of the tank wall stopped
it, so I spent about half a day with a file, curled up
alongside the cyclotron, filing a groove in the thickness
of the tank wall so that the beam could come out. This
beam is shown in the next picture. (Slide 6.) There’s
a copper fitting, which is truly a snout, since it is a
nose-shaped affair, which is fastened to the side of the
tank, and the beam comes out through it, with the
meter stick indicating the range. A little later, about
two months after this, the beam was carried farther
around — about a quarter of the way around the mag-
net. (Slide 7.) This shows where it came out of the
window, way outside the cyclotron field. This, one
might say, is the ancestor of modern beam extraction
which has become a very sophisticated art in compari-
son to what it was in those days.

Slide 7

PERSONAL ACCOUNTS

Everything up to now has been about the so-called
27-inch cyclotron. By the way, one thing I should
apologize for at some point is my concentration on
work at Berkeley. This is supposed to be the history
of the cyclotron. But, in the first place, for some time
this was the only place where there was a cyclotron,
so that’s where cyclotron history was being made.
Secondly, this talk is in honor of Professor Lawrence,
and that’s where he was doing his work. Nevertheless,
when we get to about 1936 or 1937, there did begin
to be feedback of cyclotron lore from other parts of
the world. At the end of 1936 there were about twenty
other cyclotrons in the world; so the art had spread
and things were coming back — improved ion sources,
improved arrangements of radiofrequency systems, mag-
net control circuits, and all kinds of things. And from
then on, of course, development of the cyclotron really
became an international matter. Nevertheless, I shall
continue to show pictures taken at Berkeley.

This is the 37-inch cyclotron, which used the same
magnet as the 27-inch. (Slide 8.) All one had to do was
to take out the old pole pieces, which had a reduced di-
ameter, and put in larger diameter poles and the new
tank shown on this slide. This was in late 1937 and be-
gins to show signs of professionalism. You’ll notice a
gasket groove around the top, you’ll notice nicely ma-
chined surfaces and things welded together, bolted to-
gether, and gasketed together, showing improved stand-
ards of design and construction. Still, you see a few
old-fashioned touches; I think that the tank coil on the
top side looks a bit primitive. We were still using a
simple resonant circuit and two dees, plus an induct-
ance forming the resonant circuit, which was loosely
coupled to an oscillator. With this larger diameter and

better designed tank, the deuteron energy was now up
to 8 Mev. The energy was climbing; currents were get-
ting up to 100 microamperes which were tremendous
currents at that time. Experiments were beginning to
get sophisticated. It was in 1938 that Dr. Alvarez first
introduced the method of time of flight for neutrons.
By keying the cyclotron beam and then having a gated
detector, one could use the time of flight to measure
the velocity and to select out given energy ranges.
That was the birth of that method.

Also in this period the first artificial element, tech-
netium, was discovered by Segre and Perrier, using a
piece of the cyclotron. As you know, where the beam

emerges from the dee there is a deflecting plate, and

just next to the deflecting plate the boundary of the
dee is made of a thin sheet of metal which has to de-
cide whether a given turn of the beam is inside the dee
or outside. Because the front edge of this metal sheet
gets a lot of bombardment it is always made of a
refractory metal. In this case it was made of molyb-
denum, and when the old tank was dismantled and
thrown away and the new tank went in (the one I just
showed you), Segre said he wanted the old molybdenum
strip, so we gave it to him. He was then in Italy and,

with the help of Perrier, was able to get a definite

proof that it contained the new element technetium
made by deuteron bombardment of the molybdenum.
If it hadn’t been for the fact that this particular spot
— this particular item — in the anatomy of the cyclo-
tron gets a lot of bombardment, this new discovery
would have been considerably delayed.

Another thing that started in this period is that the
theorists were getting interested in the cyclotron. Be-

266

HISTORY OF PHYSICS

fore, you see, it was an experimental art, and the people
that worked on the cyclotron sort of knew1 what they
were doing, but they weren’t very sophisticated about
it. They didn’t stop to think much about how and why
it worked; they knew that it worked and that was
enough. But it was at this time that Bethe and Rose
first pointed out the relativistic limit on cyclotron en-
ergies and, a little after that, that L. H. Thomas devised
an answer to the relativistic limit. This answer turned
out to be a little hard for the experimenters to under-
stand, so it lay fallow for many years. Now, of course,
everybody wants to build Thomas-type cyclotrons or
FFAG machines (which are, in a sense, extreme exam-
ples of Thomas cyclotrons), so it is now a great thing;
but it lay dormant for quite a while because nobody
took it very seriously at first. Also, at that time in
1937, cyclotron energies were limited by other factors
such as sizes, budgets, and things like that, and not by
the relativistic effect, which was thought of before it
became a practical limit.

Shortly after, in my history, comes the 60-inch cy-
clotron, which was the first really professionally de-
signed cyclotron that was built in Berkeley. There were
some elsew'here in the world, but this was the first in
Berkeley. Before I get to that, as a sort of transition,
I want to show a picture, taken around 1938, that

illustrates several things. (Slide 9.) Now, let’s see, what
does this illustrate? First, it illustrates that people had
started worrying about shielding against radiation
around the cyclotron. Those were 5-gallon cans that
were filled with water and simply stacked around and
above the cyclotron to give shielding. As a matter of
fact, the cans in this picture were originally on top of
the cyclotron. They developed leaks, and the people
that worked underneath would get tired of having water
drip on them, and then they would take the leaky ones
down and kick big dents in them so that nobody would
be tempted to put them back.

The second thing that this slide illustrates is the type
of building this work was done in, the Old Radiation
Laboratory. I might inject a slightly sad touch, in that
as I left Berkeley to come to this meeting, the last
boards of the Old Radiation Laboratory were being
battered down by a great big clam shell. We managed
to save a few pieces as historical relics; otherwise it is
all gone now. The third thing illustrated is that the
man pictured here is Bill Brobeck, who was our first
professional engineer hired at the Laboratory, showing
the coming in of the more professional approach to the
design and building of accelerators.

Now I will say a little about the 60-inch cyclotron,
starting with a picture that was taken in 1938, showing

Slide 10 (Left to right and top to bottom) : A. S. Langsdorf, S. J. Simmons, J. G. Hamilton, D. H. Sloan, J. R. Oppen-
heimer, W. M. Brobeck, R. Cornog, R. R. Wilson, E. Viez, J. J. Livingood, J. Backus, W. B. Mann, P. C. Aebersold,
E. M. McMillan, E. M. Lyman, M. D. Kamen, D. C. Kalbfell, W. W. Salisbury, J. H. Lawrence, R. Serber, F. N. D.
Kurie, R. T. Birge, E. 0. Lawrence, D. Cooksey, A. H. Snell, L. W. Alvarez, P. H. Abelson.

Slide 11

268

HISTORY OF PHYSICS

the magnet, which had just been installed, and (ap-
proximately) the scientific staff of the Radiation Labo-
ratory as of that time. (Slide 10.) You can see Pro-
fessor Lawrence in the center, with Professor Birge,
who was then chairman of the Physics Department, at
his right, and Dr. Cooksey at his left. There are prob-
ably quite a few people here who can recognize them-
selves in that picture. It is always a little shocking to
look at these old pictures and realize what time has
done to us all!

This is the 60-inch cyclotron shortly after it was put
together. (Slide 11.) A good many modifications in
design were embodied in this machine and one of the
most important ones is one of the things that fed back
from outside; that is, the idea of getting away from
glass insulators altogether, and having the dees plus
their stems form a resonant system which is entirely
inside the vacuum. The two tanks at the right hold the
dee stems. This system has no insulators except in the
lead-in for radiofrequency power. The power lead-ins
come down the slanting copper cylinders at the right.
The round tank on top of the magnetic yoke contains
the deflector voltage supply, a rectified voltage supply
under oil. And I think you can recognize the people
in there: Don Cooksey, Dale Corson, Ernest Lawrence,
Robert Thornton, John Backus, Winfield Salisbury,
Luis Alvarez on the magnet coil, and myself on a
dee-stem tank.

Now, just to show that physicists are not always
serious, I have made a slide of the following pose:
Laslett, Thornton, and Backus posing in the dee-stem
tank of the 60-inch cyclotron before it was assembled.
(Slide 12.) The next slide shows the control station of
the 60-inch; now we have a real control desk, designed
and not thrown together. (Slide 13.) At the desk are

Slide 12

Professor Lawrence and his brother, John Lawrence,
who initiated the medical work and is still continuing
it at the Lawrence Radiation Laboratory.

We are now up to 1939. Fission has been discovered.
I should point out that the old 37-inch cyclotron was
still running, since the 60-inch had a new magnet and
a new building, the Crocker Laboratory. So some of
these things I mention now were done on the old 37-
inch, which ran, with some interruptions, right up to the
time when it was used for the first model test on the
principle of the synchrocyclotron in 1946. But when
fission was discovered, everybody in the Laboratory
immediately jumped on the band wagon the way people
do, and tried to think of an experiment having to do
with fission. They did things with cloud chambers and
counters and and made recoil experiments and various
things of that kind.

Slide 13

PERSONAL ACCOUNTS

269

Slide 14

In 1940 came the first production of a transuranium
element, which was done with the 60-inch cyclotron,
although some of the experiments that led up to it
had been done with the 37-inch. Carbon 14, which is
perhaps the most important of all the tracer isotopes,
came in this period. Kamen and Ruben finally pinned
that down. Carbon 14 was something people had been
trying to discover for a long time. I tried once myself
but didn’t quite get it. The mass 3 isotopes, hydrogen 3
and helium 3, were discovered then, helium 3 being
found by an unusual use of a cyclotron. It was used
as a mass spectrometer rather than as a cyclotron;
that is, it was set for a resonance point for particles
with charge 2 and mass 3, and when something came
through at that resonance it had to be helium 3. This
was done by Alvarez.

Perhaps the crowning event of that time was the
award of the Nobel Prize to Professor Lawrence. Some-
body, I think Cooksey, had the foresight to take a
photograph of what appeared on the blackboard then.
(Slide 14.) You see there is a two-stage announcement:
first it says ASSOCIATED PRESS— UNCONFIRMED
and then it says CONFIRMED with an arrow. The
column down the left is a schedule of dates when people
in the Laboratory received blood counts. I see Kruger,
Corson, Alvarez, Aebersold, Livingston, Wright, Backus,
Helmholz, Salisbury, and Cooksey. That’s the other
Livingston, Bob Livingston.

Now Ernest Lawrence was never a man who wanted
to rest on achievement; he always wanted to go a step
farther. I think it w'as this forward-looking spirit, and
his ability to communicate it to others, that w'as his
true greatness. So, even though the 60-inch cyclotron
was a beautiful machine, W'as running fine, and was
doing a great deal of important work, he had this
dream of 100 million volts. I’ve looked at some of his
old correspondence and it’s always referred to as “100
million volts”; and he believed this could be achieved
with the cyclotron. When he got the Nobel Prize, this
helped things by focusing attention on this whole con-
cept, and he set out on a campaign to see if he could

Slide IS

raise the money to build a 100-million-volt cyclotron.
Of course, in those days, money was essentially private
money. There was no Manhattan District; there was
no Atomic Energy Commission; and so he was trying
to get this money by private funds.

In the course of this effort a good many things were
written, plans and calculations were made, and one
rather interesting picture was drawn which I will show
you now'. This W'as an artist’s concept of a cyclotron
for 100 million volts. (Slide 15.) This is what is now
called the 184-inch cyclotron. You can see that this
concept is rather different from the way the machine
really looks. The magnet yoke is the same, but you see
two tremendous tanks projecting on either side. Those
were the dee-stem tanks; the beam was supposed to be
deflected at one dee, make a complete turn inside, pass
through a slit in one dee stem, and emerge as shown
in the picture. But the important point this illustrates
is that one was designing this as a conventional cyclo-
tron, and one could easily estimate what dee voltages
would be required to reach a given particle voltage,
following the ideas of Rose and Bethe. We estimated
that to reach 100 million electron volts for deuterons
with this sort of design we would have wanted about

1.4 million volts between dees, or 700 000 volts to
ground on each dee. We were planning to go ahead
with floods of rf power to reach this voltage, and per-
haps we would have, who knows?

The next picture shows a conference in the Old
Radiation Laboratory, the building that has just been
torn down, between Ernest Lawrence, Arthur Compton.
Vannevar Bush, James Conant, Karl Compton, and
Alfred Loomis. (Slide 16.) They were discussing ways
of getting support for the project, and were obviously
in a happy mood. Dr. Cooksey, who took the picture,
tells me that someone had just told a joke, but the
happiness may have had a deeper justification, for a few
days later, on April 8, 1940, the Rockefeller Foundation

decided to give 1.15 million dollars for the cyclotron.
This grant, with help from the Regents of the Univer-
sity and others, made it possible for the project to
go ahead.

But then the war came along and the whole effort
of the Laboratory was diverted to other things. The
magnet for this cyclotron was used for research on
the electromagnetic isotope separation process, and it
wasn’t until quite a while later that it came back to
use as a cyclotron. By that time other ideas had come
out — the idea of the use of phase stability and fre-
quency modulation — and so when the machine finally
was built as a cyclotron, it didn’t look like that picture
on Slide 15 but looked like this one. (Slide 17.) Here

PERSONAL ACCOUNTS

271

Slide 18

Slide 19

is what the 184-inch cyclotron looked like when it was
first assembled. You can get some idea of the size,
since there’s a man there for scale. Of course, by now
this is a synchrocyclotron. When I think of the history
of the cyclotron in the sense of this talk, I think of it
as the history of the fixed frequency cyclotron, so I
won’t say much more about this machine except that
it does work. I’ll show you a picture of about the way
it looks today, encased in concrete blocks for shielding,
which is a better solution to the shielding problem than
5-gallon cans of water. (Slide 18.) If you look hard,
you can see a man in this picture, too.

I shall close this talk with an aerial view of the
present establishment in Berkeley of the Lawrence
Radiation Laboratory. (Slide 19.) In the foreground,
in the circular building, is the Bevatron, which is of
course a descendant of the cyclotron since it does use
the magnetic resonance principle. A little farther back
is another circular building which houses the 184-inch
cyclotron, the machine I just showed you. The other
buildings house other accelerators, research laboratories,
shops, and all the things which make up the labora-
tory which really, one can say in all truth, is the out-
growth of the ideas and the faith and the strength of
Professor Lawrence, in whose memory we have spoken
today.

272

HISTORY OF PHYSICS

Otto R. Frisch, professor of natural
philosophy ( physics ) at Cambridge
University, England, did research in
Berlin (1927-30), Hamburg (1930-
33), London ( 1933-34), Copen-
hagen ( 1934-39 ) and Birmingham
( 1939-40 ) . During the war he
worked on the A-bomb at Los
Alamos. He was first to observe
energy liberated in the fission of a
single uranium nucleus.

John A. Wheeler, one of the first
American scientists to concentrate
on nuclear fission, worked at the
U. of Copenhagen in 1934 as a
National Research Fellow with
Niels Bohr. Wheeler received his
PhD in physics at the Johns
Hopkins University prior to his
research in Copenhagen. In 1938
he joined Princeton’s physics de-
partment, where he remains active.

The Discovery of Fission

Initial formulations of nuclear fission are colored
with the successes, failures and fust plain bad luck of several scientists
from different nations. The winning combination of good
fortune and careful thought made this exciting concept a reality.

by Otto R. Frisch and John A. Wheeler

PHYSICS TODAY / NOVEMBER 1967

How It All Began

by Otto R. Frisch

The neutron was discovered in 1932.
Why, then, did it take seven years be-
fore nuclear fission was found? Fission
is obviously a striking phenomenon; it
results in a large amount of radioactiv-
ity of all kinds and produces fragments
that have more than ten times the total
ionization of anything previously
known. So why did it take so long?
The question might be answered best
by reviewing the situation in Europe
from an experimentalist’s point of
view.

Research in Europe

In Europe there were few laboratories
in which nuclear-physics research was
conducted, and I think the word
“team” had not yet been introduced
into scientific jargon. Science was
still pursued by individual scientists
who worked with only one or two stu-
dents and assistants.

Paris harbored some of the most ac-
tive research laboratories in Europe.
It is the city in which radioactivity
had been discovered and where Ma-
dame Curie was working until her
death in 1934. She still dominated
the situation: Techniques were quite
similar to those used at the turn of the
century; that is, ionization chambers
and electrometers. This state of af-
fairs is good enough for performing ac-
curate measurements on natural ra-
dioactive elements, but it is not really
adequate for much of the work on nu-
clear disintegration. Madame Curie

had little respect for theory. Once,
when one of her students suggested an
experiment, adding that the theoreti-
cal physicists next door thought it
hopeful, she replied, “Well, we might
try it all the same.” Their disregard
of theory may have cost them the dis-
covery of the neutron.

Cambridge is the second place wor-
thy of discussion. Ernest Rutherford,
whose towering personality dominated
Cambridge research, had split atomic
nuclei in 1919; since 1909 he had, in
fact, been keenly concerned with the
observation and counting of individual
nuclear particles. He first introduced
the scintillation method and stuck
firmly to it. His great preference was
for simple, unsophisticated methods,
and he possessed a strong distrust of
any complicated instrumentation.
Even in 1932, when John Cockcroft
and Ernest Walton first disintegrated
nuclei by artificially-accelerated pro-
tons, they used scintillations to detect
the process. By that time Rutherford
had realized that electronic methods
of particle counting must be devel-
oped. The reason was that the scin-
tillation method clearly had its short-
comings. It did not work for very low
or high counting rates and was not
really reliable. This deficiency was
highlighted by the results that came
from the third laboratory I want to
mention— Vienna.

Vienna is where I began my career
and it was in those days a sort of en-

PERSONAL ACCOUNTS

273

fant terrible of nuclear physics. Sev-
eral physicists were claiming that not
only nitrogen and one or two others of
the light nuclei could be disintegrated
by alpha particles but that practically
all of them could and did give many
more protons than anybody else could
observe. I still do not know how they
found these wrong results. Apparent-
ly they employed students to do the
counting without telling them what to
expect. On the face of it, that opera-
tion appears to be a very objective
method because the student would
have no bias; yet the students quickly
developed a bias towards high num-
bers because they felt that they would
be given approval if they found lots of
particles. Quite likely this situation
caused the wrong results along with a
generally uncritical attitude and con-
siderable enthusiasm over beating the
English at their own game.

I still remember when I left Vienna
at just about that time (after having
escaped the duty of counting scintilla-
tions ) . My supervisor, Karl Przibram,
told me with sadness in his voice, “You
will tell the people in Berlin, won’t
you, that we are not quite as bad as
they think?” I failed to persuade
them.

Germany had nuclear-physics re-
search in several places. The team of
Otto Hahn and Lise Meitner, which
had been one of the first groups to
study radioactive elements, had at that
time separated to carry out indepen-

dent research. Hahn was working on
various applications of radioactivity
for the study of chemical reactions,
structures of precipitates and similar
subjects, whereas Lise Meitner was
using radioactive materials chiefly to
elucidate the processes of beta and
gamma emission and the interaction of
gamma rays with matter.

In addition, Hans Geiger was in
Germany. He had been with Ruther-
ford from 1909 onwards, in the early
days before the nucleus was discov-
ered. Rutherford felt uncertain about
the scintillation method and asked
Geiger to develop an electric counter
to check on it. But as soon as Ruther-
ford saw that the two gave the same
results, Rutherford returned to the
scintillation method, which appeared
to be simpler and more reliable when
used with proper precaution. Geiger
went back to Germany and perfected
his electric counters, and in 1928, to-
gether with a student named
W. Muller, he developed an improved
counter that could count beta rays.
Earlier counters were inadequate for
this purpose, and scintillation methods
were also incapable of detecting beta
rays. However the new counters were
still very slow because the discharge
between the central wire and the cy-
lindrical envelope was quenched by a
large resistor of many megohms placed
in the circuit; consequently the count-
ing rate was limited to numbers not
much greater than with the scintilla-

tion method. Even at a few hundred
particles a minute there were quite
large corrections to be applied.

Walther Bothe was the first to use
the coincidence method, both in an at-
tempt to do something about cosmic
rays and also for measuring the energy
of gamma rays by the range of the sec-
ondary electrons they produced. This
was really the first reliable method for
measuring the energy of weak gamma
radiations.

Until 1932, the only source of par-
ticles for doing atomic nuclear disinte-
gration was natural alpha particles:
either polonium, which was difficult
to come by (in fact one practically
had to go to Paris ) or sources of one of
the short-lived decay products of radi-
um, which were very clean but were
short-lived and usually had lots of
gamma radiation.

The year of discovery

But in 1932, that annus mirabilis, not
only the neutron was discovered but
two other developments took place.
In the US Ernest O. Lawrence made
the first cyclotron that showed prom-
ise of being useful, and in England
Cockcroft and Walton built the first
accelerator for protons capable of pro-
ducing nuclear disintegrations. I
need not state that this was the begin-
ning of an enormous development;
most of nuclear physics as we know it
would have never come about without
at least one of those two instruments.
But the interesting thing is that they
played practically no role in that nar-
row thread that led to the discovery of
nuclear fission.

I do not want to dwell on the dis-
covery of the neutron very much be-
cause it was discussed in several inter-
esting lectures in 1962 at the History
of Science Congress held in Ithaca,
New York. The published proceed-
ings contained interesting contribu-
tions by Norman Feather and Sir
James Chadwick, who showed that the
neutron was discovered in Cambridge,
not simply by chance with everybody
else having done the groundwork, but
because a search for the neutron had
been going on in Cambridge (admit-
tedly with wrong ideas) . The people
at Cambridge were keyed up for this
discovery. They had made one obser-
vation that was important and that
tends to be overlooked: H. C. Web-

COMPUTATIONS, indicating chains of radioactive elements, were published in a
1938 Die N aturwissenschaften article by Hahn, Meitner and Strassmann. — FIG. 1

274

HISTORY OF PHYSICS

GREAT AND GOOD FRIENDS. Lord and Lady Rutherford (left) with
Niels and Margrethe Rohr in Rutherford’s garden. The photograph was
taken about 1930.

ster showed that those queer pene-
trating rays that beryllium emitted
when alpha particles fell on it were
more intense in the forward direction
than in the backward direction. This
result was quite incomprehensible if
the radiation were gamma rays as ev-
erybody believed. Even the French
physicists Curie and Joliot shared that
belief in the teeth of all theoretical
predictions. Then Chadwick’s experi-
ment showed clearly that the mysteri-
ous radiation consisted of particles hav-
ing approximately the mass of the pro-
ton. There was a bit of confusion at
the time because the word “neutron”
had been used by Enrico Fermi and
Wolfgang Pauli to indicate the particle
that later came to be called the “neu-
trino.”

After the neutron was discovered,
there was of course a certain rush of
activity, but nobody knew quite what
to do. Neutrons were rather few in
number. They were, after all, secon-
dary products of nuclear disintegra-
tion. With only natural alpha sources
available at first, neutron production
was low.

Moreover the main instrument for
detection was essentially the cloud
chamber. With cloud chambers only
a limited number of tracks due to neu-
trons could be found. And it was
slow work to make any sense out of
the few detected tracks of recoil nu-
clei. Leo Szilard once joked that if a
man suddenly does something unex-
pected there is usually a woman be-
hind it, but if an atomic nucleus sud-
denly does something unexpected,
there is probably a neutron behind it.

Electronic counting methods had
only just been developed; largely as a
reaction to the wrong results coming
out of Vienna that nobody else could
confirm, it had been decided that it
really was necessary to build electron-
ic. amplifiers and counters. Actually
the Viennese themselves started that
kind of work but were not very suc-
cessful. The work was also started in
Switzerland with some success by
Hermann Greinacher. Yet I think the
main thread that led to the develop-
ment of decent counters took place in
England, where Charles Wynn-Wil-
liams used proper screening and tubes
with low noise level etc. to produce
electronic counters. Nevertheless
those counters, although Chadwick

had used them with good effect to pin
down the neutron, were still too noisy
to be of much use.

Artificial radioactivity

Things really got moving when, in
1934, artificial radioactivity was found
by Curie and Joliot. I think they must
have been very happy to have made
up for their failure to spot the neutron
two years previously. Almost to the
day two years previously both discov-
eries came out in the middle of Janu-
ary. They had known for many
months before that aluminum bom-
barded with alpha particles emits posi-
trons, but it had never occurred to
them that this might be a delayed
process. They had only observed the
positron during bombardment. Law-
rence and his cyclotron people in Cali-
fornia had made the same mistake. In
fact they had noticed that the counters
misbehaved after the cyclotron was
switched off. I am told that they
built in special gadgetrv so that the
counters were automatically switched
off together with the cyclotron! Oth-
erwise they would have found artifi-

cial radioactivity before the French.

It is astonishing that nobody ap-
pears to have thought beforehand that
the result of a nuclear disintegration
might be an unstable nucleus although
the existence of unstable nuclei had, of
course, been known for thirty years or
more. I have been told that, after the
discovery, Rutherford wrote to Joliot
and congratulated him on his discov-
ery saying that he himself had thought
that some of the resulting nuclei might
be unstalrle, but had always looked for
alpha particles only because he was
not really interested in beta particles.

As soon as this work became known
in January 1934 a lot of people rushed
to repeat and extend the experiment.
But most of them rushed in a straight
line indicated by Curie-Joliot, bom-
barding other elements with alpha
particles. (So did I in Blackett’s labo-
ratory in London.)

But in Rome Fermi at that time had
already decided that nuclear physics
was an important and interesting line,
and he had started to set up some in-
strumentation. So when this discoverv
came along, he began working quite

PERSONAL ACCOUNTS

275

fast to see whether neutrons would
form radioactive nuclei.

I remember that my reaction and
probably that of many others was that
Fermi’s was a silly experiment because
neutrons were much fewer than alpha
particles. What that simple argument
overlooked of course was that they are
very much more effective. Neutrons
are not slowed down by electrons, and
they are not repelled by the Coulomb
field of nuclei. Indeed, within about
four weeks of the discovery by Curie
and Joliot, Fermi published the first
results proving that various elements
did become radioactive when bom-
barded with neutrons. Only another
month later he announced that bom-
barding uranium produced some new
radioactivity that he felt must be due
to transuranic elements. Because
both on theoretical grounds (Coulomb
barrier and all that) and as far as the
experiments confirmed it, all heavier
elements were known to absorb neu-
trons without splitting anything off.
And so it was felt that must also be the
case with uranium.

This work was of course considera-
bly interesting to radiochemists. Sev-
eral took it up, but once again, oddly
enough, one false result started things
really moving— a note by Aristid von
Crosse, a German-born chemist work-
ing in the US, who thought one of
these elements behaved like protactin-
ium. He had done some of the early
work with Hahn on protactinium soon
after it was discovered in 1917; so his
suggestion put Hahn and Meitner on
their mettle. They felt protactinium
was their own baby and they were
going to check it. Lise Meitner per-
suaded Hahn to join forces again.
They soon showed that von Grosse
was wrong: It was not protactinium.
On the other hand there were so many
odd things there that they were cap-
tured by this phenomenon and had to
go on. The results were most pecu-
liar.

Figure 1 shows one of the tabula-
tions indicating the chains of radioac-
tive elements that Hahn and Meitner
had thought identified them. They
did not give new names to the trans-
uranic elements that they thought
they had identified, but they used the
prefix “eka” to indicate that they were
higher homologues of rhenium, os-
mium, etc. up to ekagold. Obvious-

LINKS IN THE CHAIN. Cockcroft
(top) and Walton contributed to the
new ideas when they disintegrated
nuclei by artificially-accelerated pro-
tons.

ly, Hahn was excited to have a whole
new lot of chemical elements to play
with and to study their properties.
Today, of course, these elements after
uranium are known as neptunium, plu-
tonium, americium etc., and are
known to be chemically quite different
from those that Hahn was studying.

Parallel chains

The results were astonishing for two
reasons. In the first place, it ap-
peared that there were three parallel
series. And from the yields obtained

they must all derive from uranium 238
or possibly one of them from 235
(which is already much rarer). So it
looked as if there were at least two
parallel chains of isomeric elements.
This isomeric property had to be prop-
agated all along the chain of beta
disintegrations.

Nuclear isomerism was still fairly
new in 1938, and its interpretation
was not altogether clear. It had been
suggested (as we now accept) that it
was due to high angular momentum,
but there were also proposals that it
might be due to the existence of rigid
structures inside nuclei. One could
imagine that such a rigid structure
might survive a beta decay and might
influence the half-life of the subse-
quent product.

But then there was still the mystery
of the great length of those chains.
Uranium, after all, was not beta un-
stable itself. The other elements in
that region never had more than two
beta decays in succession; yet here
four or five had been found. So Hahn
the chemist was delighted by so many
new elements, but Hahn the radio-
physicist or radiochemist was rather
worried about the mechanism that
could account for them.

All this work was made difficult by
the political situation in Germany.
Hitler was in power and the institute
had to play a delicate game of politics
to prevent racial persecution from re-
moving some of its personnel. In
1938, when Austria was occupied by
the Nazis, Lise Meitner felt very inse-
cure; rumors began to float around
that she might lose her post and be
prevented thereafter from leaving
Germany because of her knowhow. A
certain amount of panic resulted.
Dutch colleagues offered to smuggle
her to Holland without a visa. Thus
she left Germany in the early summer
of 1938, went from Holland for a brief
stay in Denmark, and was offered hos-
pitality by Manne Siegbahn at the
Nobel Institute in Stockholm.

Near misses

After that, the team that had already
brought Strassmann in with Hahn as a
second chemist had to carry on with-
out her. In the meantime some work
had been started in Paris. It is inter-
esting that they had a different angle.
They were at first not so interested in

276

the transuranic elements; but they
realized that if thorium is bombarded
with neutrons, one ought to find the
beginning of the new and missing ra-
dioactive chain with the atomic
weight 4n 1. One realizes that the
others, 4n, 4n + 2, 4n + 3, are all
represented by the natural radioactive
series. But the 4n + 1 was missing,
and so Irene Curie, the daughter of
Madame Curie, together with Hans
von Halban, an Austrian, and Peter
Preiswerk, a Swiss, set out to search
for that series and published some
work on it.

Later that team broke up because
Halban came to Copenhagen and, for
a time, worked with me on the study
of slow neutrons. Irene Curie found a
new collaborator in Pavel Savitch, a
Yugoslav. They tried to disentangle
the transuranic elements. Having
realized that there was a great variety
of different materials, Irene Curie had
the good idea of selecting one of them
simply by the high penetration of its
beta rays. They covered their
samples with a fairly thick sheet of
brass and only studied the substance
whose radiation penetrated. They did
not realize that even that method
might not select a single substance al-
though the substance appeared to
have a reasonably unique lifetime of
3.5 hours. From the chemical behav-
ior they first thought it looked like tho-
rium.

This work was checked by Hahn,
who concluded that it was not thorium
and wrote so to Paris. Curie and Sav-
itch continued the work and in a later
paper in the summer of 1938 acknowl-
edged that the 3.5-hour substance was
not thorium but behaved a bit more
like actinium and even more like lan-
thanum. She had come very close in-
deed to the concept of nuclear fission
but unfortunately did not state it
clearly. She said that it was definitely
not actinium and that it was quite sim-
ilar to lanthanum, “from which it could
be separated only by fractionation.”
But she did think it could be sepa-
rated. The reason was probably that
she still had a mixture of two substan-
ces; in that case of course one does ef-
fect a partial separation. Then this
work was in turn checked by Hahn
and Strassmann who discovered ra-
dioactive products that behaved partly
like actinium, partly a bit like radium.

There was another near miss at
about the same time: Gottfried von
Droste, a physicist working with Lise
Meitner, looked for long-range alpha
rays from uranium during neutron
bombardment. If he had supressed
the ordinary alpha rays by applying a
bias to the amplifier, he would not
have failed to find fission. Unfortu-
nately instead of using a bias he used a
foil, and that foil was thick enough to
stop not only uranium alpha rays but
also the fission fragments; nor did he
find any long-range alpha rays, which
had to be there if radium or actinium
isotopes were formed.

Then Hahn and Strassmann checked
the chemical properties of this “ra-
dium” with care and found that they
were identical with those of barium.

A propitious visit

This is where I came in because Lise
Meitner was lonely in Sweden and, as
her faithful nephew, I went to visit her
at Christmas. There, in a small hotel
in Kungalv near Goteborg I found
her at breakfast brooding over a letter
from Hahn. I was skeptical about the
contents— that barium was formed
from uranium by neutrons— but she
kept on with it. We walked up and
down in the snow, I on skis and she
on foot (she said and proved that she
could get along just as fast that way),
and gradually the idea took shape that
this was no chipping or cracking of
the nucleus but rather a process to be
explained by Bohr’s idea that the nu-
cleus was like a liquid drop; such a
drop might elongate and divide it-
self. Then I worked out the way the
electric charge of the nucleus would

diminish the surface tension and found
that it would be down to zero around
Z = 100 and probably quite small for
uranium. Lise Meitner worked out
the energies that would be available
from the mass defect in such a break-
up. She had the mass defect curve
pretty well in her head. It turned out
that the electric repulsion of the frag-
ments would give them about 200
MeV of energy and that the mass de-
fect would indeed deliver that energy
so the process could take place on a
purely classical basis without having
to invoke the crossing of a potential
barrier, which of course could never
have worked.

We only spent two or three days to-
gether that Christmas. Then I went
back to Copenhagen and just managed
to tell Bohr about the idea as he was
catching his boat to the US. I remem-
ber how he struck his head after I had
barely started to speak and said:
“Oh, what fools we have been! We
ought to have seen that before.” But
he had not— nobody had.

Lise Meitner and I composed a
paper over the long-distance tele-
phone between Copenhagen and
Stockholm. I told the whole story to
George Placzek, who was in Copenha-
gen, before it even occurred to me to
do an experiment. At first Placzek
did not believe the story that these
heavy nuclei, already known to suffer
from alpha instability, should also be
suffering from this extra affliction.
“It sounds a bit,” he said, “like the
man who is run over by a motor car
and whose autopsy shows that he had
a fatal tumor and would have died
within a few days anyway.” Then he

k

a

THE JOLIOT-CURIES discovered
artificial radioactivity.

CENTRAL FIGURES in the discovery were Otto Hahn and Lise Meitner,
here shown in front of the institute that bears their names

said, “Why don’t you use a cloud
chamber to test it?” I did not have a
cloud chamber handy and thought it
would be difficult anyway. But I
used an ionization chamber and it was
a very easy experiment to observe the
large pulses caused by ion fragments.

I do not think chronology means
very much and certainly cannot claim
any particular intelligence or original-
ity. I was just lucky to be with Lise
Meitner when she received advance
notice of Hahn’s and Strassmann’s dis-
covery. Then I had to be nudged be-
fore I did the crucial experiment on 13
January. By that time our joint paper
was nearly written. I held it back for
another three days to write up the
other paper, and then they were both
sent to Nature on 16 January but pub-
lished a week apart. In the first paper
I used the word “fission” suggested to
me by the American biologist, William
A. Arnold, whom I asked what one
calls the phenomenon of cell division.

The second paper also contained a
suggestion from Lise Meitner that fis-
sion fragments emerging from a bom-
barded uranium layer could be collect-
ed on a surface and their activity
measured. The same thought inde-
pendently occurred to Joliot, and he
successfully did this experiment on 26
January. About that same time the
news reached the US; what happened
then is discussed by Wheeler.

Serendipitous searches

To come back to my initial question:
Why did it take so long before fission
was recognized? Indeed, why wasn’t
the neutron found earlier? Ruther-
ford thought about it and foretold
some of its properties as early as his
Bakerian lecture in 1920; but Joliot
did not read it, expecting a public lec-
ture to contain nothing new! When
Curie and Joliot found that the “beryl-
lium radiation” ejected protons from
paraffin, they put it down to a kind of
Compton effect of a very hard gamma
radiation (some 50 MeV), ignoring
the objections of theoretical physicists.
The neutron was finally observed in
Cambridge, where such a particle was
expected and had been sought.

At the time the neutron was found
in 1932 pulse amplifiers and ionization
chambers were available for a facile
detection of fission pulses. But that
would have been too big a jump to ex-
pect. The liquid-drop model of the
nucleus was born late; the compound-
nucleus idea was conceived by Bohr
only late in 1936. It would have been
a stroke of genius to think of fission
then, and nobody did.

The discovery of artificial radioac-
tivity in 1934 was again a chance dis-
covery; no one had looked for it ex-
cept Rutherford, who looked in vain
for alpha decay. And indeed the

Berkeley team turned a blind eye
when their counters “misbehaved.”
After the discovery there was a
sheep-like rush to repeat the experi-
ment with only the most obvious vari-
ation (I was one of the sheep). Only
Fermi had the intelligence to strike
out in a different and tremendously
fruitful direction.

But then Fermi got on the wrong
track: He felt sure that uranium, like
other heavy nuclei, would obediently
swallow any slow neutron that fell on
it. He did make sure that the radioac-
tive substances that were formed from
it were different from any of the
known elements near uranium. Ida
Noddack, a German chemist, quite
rightly pointed out that they might be
lighter elements; but her comments
(published in a journal not much read
by chemists and hardly at all by physi-
cists) were regarded as mere pedant-
ry. She did not indicate how such
light elements could be formed; her
paper had probably no effect whatev-
er on later work.

In the end it was good solid chemis-
try that got things on the right track.
Irene Curie and Pavel Savitch came
very close to it; only the presence of
two substances with maliciously simi-
lar properties prevented them from es-
tablishing uranium fission before
Hahn and Strassman finally accom-
plished it. □

278

HISTORY OF PHYSICS

Mechanism of Fission

by John A. Wheeler

In early January 1939 the Swedish-
American liner, MS Drottningholm
carried a short message across the
stormy sea from Copenhagen to New
York. This message symbolized the
steady transfer of nuclear discoveries
from Europe to the US that had been
going on during the Hitler years.

Although these transfers were fate-
ful for the US and the rest of the
world, the act of relaying this particu-
lar message was simple: words of Otto
Frisch to Niels Bohr and Leon Rosenfeld
at Copenhagen before departure and
words spoken by Rosenfeld to me that
Monday afternoon, January 16, when I
met them at the pier, and by Bohr to me
when he and I started working on the
issue the next day at Princeton.
As a junior participator in the events
that occurred then and in subsequent
months, I shall relate the activities that
led to the publication of a Physical Re-
view paper by Bohr and me. In this
paper we summarized the thoughts
expressed in the message: the liquid-
drop model that Frisch had applied to
the mechanism of fission and the de-
terminations of packing fraction that
Lise Meitner considered when arriving
at the first estimate of energy release in
fission.

No one looking at such a novel
process at that time could fail to call
on everything he knew about nuclear
physics to seek an interpretation. For-
tunately the key ideas for unraveling
the puzzle had already been de-
veloped. It may be appropriate to
recall what had been learned about
nuclear physics in the preceding half
a dozen years.

Clues to the answer
1933 was a fruitful year for someone
like me, who was just earning his doc-
tor’s degree. It was the year of the
discovery of the neutron and Werner
Heisenberg’s great paper on the struc-
ture of nuclei built out of neutrons and
protons. These discoveries made one
feel that he might soon know as much
about the nucleus as he already knew
about the atom.

Encouraged by the vision that in-
spired so many young men, me in-

cluded, at that time, I spent 1933-34
working with Gregory Breit, to whose
insights I owe so much. He and the
group of which I soon found myself a
member accepted almost unconsciously
the model of the nucleus of that day:
neutrons and protons moving in a com-
mon self-consistent potential, closely
analogous to the electric potential of
the atom. “Unconscious” our accept-
ance of the model was, yes; but also
shadowy. None of us took it too liter-
ally, especially not Breit, with his cau-
tion and insight. Thus he was always
willing to consider alpha particles in
the nucleus as well as neutrons and
protons when that point of view made
sense in considering a particular reac-
tion. Breit also directed especial at-
tention to areas of investigation as
nearly free as possible of model-de-
pendent issues. Thus much work was
done on the penetration of charged
particles into nuceli and how the cross
section for a nuclear reaction depends
on energy. The analysis of scattering
processes in terms of phase shifts also
received much attention.

With Breit’s warm endorsement I
spent the following year at Niels Bohr’s
institute in Copenhagen. Here I was
initiated into the study of many new
ideas, but nothing was more impressive
in nuclear physics than the message
that Mpller brought back during the
spring of 1935 from a short Easter visit
to Rome: It told of Fermi’s slow-neu-
tron experiments and the astonishing
resonances that he had discovered.
Every estimate ever made before then
indicated that a particle passing
through a nucleus would have an ex-
tremely small probability of losing its
energy by radiation and undergoing
capture if the current nuclear model
was credible. Yet, directly in opposi-
tion to the predictions of this model,
Fermi’s experiments displayed huge
cross sections and resonances that were
quite beyond explanation.

Of course a number of weeks went
by before the most significant results
of this discovery could be sorted out.
Everyone was actively concerned, but
no one more so than Bohr, who paced

up and down in the colloquium and
took a central part in discussions.

Liquid drops

The story of the development of the
liquid-drop model and the compound-
nucleus picture is a familiar one.
What is not so clear and was certainly
not evident at the time is the distinc-
tion between these ideas: (1) The
compound-nucleus model shows, in
essence, that the fate of a nucleus is
independent of the mechanism by
which it has been formed, and (2) the
liquid-drop model is, so to speak, a
special case of the compound-nucleus
model, a particular way of making
such a model of nuclear structure rea-
sonable. Bohr proposed that the mean
free path of nucleon is short in rela-
tion to nuclear dimensions instead of
being long, as assumed in all previous
estimates. This new idea made some-
thing like a liquid-drop model exceed-
ingly attractive.

No one looking back on the situation
from today’s vantage point can fail to
be amazed at “the great accident of
nuclear physics”— the circumstance that
the mean free path of particles in the
nucleus is neither extremely short com-
pared with nuclear dimensions (as as-
sumed in the liquid-drop picture) nor
extremely long (as assumed in the
earlier model) but of an intermediate
value. Moreover, all the marvelous
detail of nuclear physics turns out to
depend in such a critical way on the
value of this parameter. As Aage Bohr
and Ben Mottelson have taught us in
recent years, no one could have pre-
dicted the precise one among many
alternative regimes in which the
phenomenology would actually lie
from any advance estimate of the
mean free path. Only observation
could suffice! Knowing as little as
one did in 1935 about the value of
this decise parameter, still less about
its cirticality, one had no option but
to explore with all vigor the idea that
the mean free path is very short.

The development of the liquid-drop
model, which was applied to a variety
of processes, took place in the hands
of Fritz Kalckar and Niels Bohr in
1935-37. They applied it to a variety
of processes. At the center of every
such application stood the idealization
of the compound nucleus, that is, the
concept that a nuclear reaction occurs

STROLLING THINKERS, Fermi (left) anil Bohr, are well known for
their important applications and expansions of early ideas of nuclear fission.

in two well separated stages: First,
the particle arrives in the nucleus and
imparts an excitation; then in some
way the nucleus uses that energy for
radiation, neutron or alpha-particle
emission or any other competing pro-
cess.

Bohr brings the news

The message that Frisch gave Bohr
as Bohr left Copenhagen opened up a
new domain of application for this
concept of the compound nucleus. By
the time Bohr had arrived in New York
he had already recognized that fission
is one more process in competition with
neutron reemission and gamma-ray
emission. Four days after his arrival
he and Rosenfeld finished a paper sum-

marizing this general picture of fission
in terms of formation and breakup of
the compound nucleus.

Rosenfeld had originally accom-
panied Bohr to Princeton for several
months of work on the problem of
measurement in quantum electrody-
namics. During Rosenfeld’s Princeton
sojourn Bohr gave less than half a
dozen lectures on that issue. Never-
theless, that and many other questions
conspired to take much of his time.
No one could go into his office without
seeing the long list of duties and people
he had to give time to. That list made
it easy to appreciate the pleasure with
which he came into my office to discuss
the work that we had under way. We
were trying to understand in detail the

mechanism of fission and, not least,
analyze the barrier against fission and
the considerations that determine its
height.

First of all, of course, we had to
formulate the very idea of a threshold
or barrier. How can there even be
any barrier according to the liquid-
drop picture? Is not an ideal fluid
infinitely subdivisible? And therefore
cannot the activation energy required
to go from the original configuration to
a pair of fragments be made as small
as one pleases? We obtained guidance
on this question out of the theory of
the calculus of variations in the large,
maxima and minima, and critical
points. This subject we absorbed by
osmosis from our environment, so
thoroughly charged over the years by
the ideas and results of Marston Morse.
It became clear that we could find a
configuration space to describe the de-
formation of the nucleus. In this de-
formation space we could find a
variety of paths leading from the nor-
mal, nearly spherical configuration over
a barrier to a separated configuration.
On each path the energy of deforma-
tion reaches a highest value. This
peak value differs from one path to
another. Among all these maxima the
minimum measures the height of the
saddle point or fission threshold or
activation energy for fission.

While we were estimating barrier
heights and the energy release in vari-
ous modes of fission, the time came for
the fifth annual theoretical physics con-
ference held in Washington on 26 Jan.
Bohr felt a responsibility toward Frisch
and Meitner and thought that word of
their work-in-progress and their con-
cepts should not be released until they
had the proper opportunity to publish,
as is the custom throughout science.
Even though this was the situation, at
the outset Rosenfeld did not appreciate
all the complications and demands of
Bohr’s position. On the day of Bohr’s
arrival in the US Rosenfeld went down
to Princeton on the train. (Bohr had
an appointment later that day in New
York.) Rosenfeld reported the new
discovery at the journal club— the regu-
lar Monday night journal club— and of
course everybody was very excited.
Isidor I. Rabi, who was at the journal
club, carried the news back to Colum-
bia, where John Dunning started to
plan an experiment.

Nevertheless, even on 26 Jan., Bohr
was reluctant to speak about Frisch’s
and Meitner’s findings until he re-
ceived word that they had actually
been published. Fortunately that
afternoon an issue of Die N aturwissen-
schaften, which contained work by
Hahn and Fritz Strassmann, was
handed to him; thus he could tell about
it. Of course everybody started his
experiments. The first direct physical
proof that fission takes place appeared
in the newspapers of the twenty-ninth.

Shaping the theory

The analysis of fission led to the theory
of a liquid drop and this in turn led
back to a favorite love of Bohr, who,
for his first student research work, ex-
perimented on the instability of a jet
of water against breakup into smaller
drops. He was quite familiar with the
work of John W. Strutt, the third Lord
Rayleigh. This work furnished a start-
ing point for our analysis. However,
we had to go to terms of higher order
than Rayleigh’s favorite second-order
calculations to pass beyond the purely
parabolic part of the nuclear potential,
that is, the part of the potential that
increases quadratically with deforma-
tion. We determined the third-order
terms to see the turning down of the
potential. They enabled us to evalu-
ate the height of the barrier, or at least
the height of the barrier for a nucleus
whose charge was sufficiently close to
the critical limit for immediate break-
up.

Here we found that we could reduce
the whole problem to finding a func-
tion / of a single dimensionless variable
x. This “fissility parameter” measures
the ratio of the square of the charge to
the nuclear mass. This parameter has
the value 1 for a nucleus that is already
unstable against fission in its spherical
form. For values of x close to 1, by the
power-series development mentioned
above one could estimate the height of
the barrier and actually give quite a
detailed calculation of the first two
terms in the power series for barrier
height, or /, in powers of (1 — x) .
The opposite limiting case also lent it-
self to analysis. In this limit the nu-
cleus has such a small charge that the
barrier is governed almost entirely by
surface tension. The Coulomb forces
give almost negligible assistance in
pushing the material apart.

ROSENFELD, with Bohr, summarized
the idea of fission.

Between this case ( the power series
about * = 0) and the other case (the
power series about x = 1) there was
an enormous gap. We saw that it
would take a great amount of work to
calculate the properties of the fission
barrier at points in between. Conse-
quently we limited ourselves to inter-
polation between these points. In the
28 years since that time many workers
have done an enormous amount of
computation on the topography of the
deformation energy as depicted over
configuration space as a “base” for the
topographic plot. We are still far from
completing the analysis. Beautiful
work by Wladyslaw J. Swiatecki and
his collaborators at Berkeley has taught
us much more than we ever knew be-
fore about the structure of this fission
barrier and has revealed many unsus-
pected features for values of x that
are remote from the two simple, origi-
nal limits.

From fission barrier we turned to
fission rate. All of us have always
recognized that nuclear physics con-
sists of two parts: (a) the energy of a
process and (b) the rate at which the
process will go on. The compound-
nucleus model told us that the rate
should be measured by the partial
width of the nuclear state in question
for breakup by the specified process.

Toward a simpler theory

How could we estimate this width?
Happily, in earlier days, several per-
sons in the Princeton community—
among them Henry Eyring and Eugene
Wigner— had been occupied by the
theory of the rates of chemical reac-

tions. Also we derived some useful
information from cosmic-ray physics.
Who does not recall the many detailed
calculations Stprmer and his associates
made on the orbits of cosmic-ray par-
ticles in the earth’s magnetic field?
Fortunately Manuel Sandoval Vallarta
and later workers were able to spare
themselves almost all of these details.
They had only to employ Liouville’s
theorem. It said that the density of
systems in phase space remains con-
stant in time.

The same considerations of phase
space were equally useful for evaluat-
ing the rate of fission. It turned out
that we could express the probability
of going over the barrier as the ratio of
two numbers. One of these numbers is
related to the amount of phase space
available in the transition-state con-
figuration as the nucleus goes over the
top of the barrier. We were forced to
think of all the degrees of freedom of
the nucleus other than the particular
one leading to fission. All these other
degrees of freedom are summarized
in effect in the internal excitations of
the nucleus as it passes over the fission
barrier. In classical terms this con-
cept is well defined. It is a volume
in phase space completely determined
by the amount of energy.

The other quantity, appearing in the
denominator of the rate-of-fission ex-
pression, is linked with the volume of
phase space accessible to the com-
pound system. In all the complex
motion short of actual passage over the
barrier the ensemble of systems under
consideration remains confined to the
narrow band of energies, aE, defined
by the energy of the incident neutron.
What counts is this energy interval
multiplied with the rate of change of
volume in phase space with energy
for the undissociated nucleus. The
beauty of this derivation is the fact that
these classical ideas lend themselves
to direct transcription into quantum-
mechanical terms. Thus the Went-
zel-Kramers-Brillouin approximation
taught us that volume in phase space
determines the number of energy
levels. So we concluded that the
width— the desired width measuring
the probability for fission— is given by
a ratio in which the numerator is the
number of states accessible to the
transition-state nucleus as it is going
over the barrier, that is, the number of

PLACZEK was helpful in formulating
theories of fission.

states of excitation other than motion
in the direction of fission. In the de-
nominator appears the spacing be-
tween nuclear energy levels, divided
by 2tt. Thus we had attained the most
direct tie with experimentally interest-
ing quantities. The formula that was
obtained in this way for the reaction
rate, or the level width, applied to a
wide class of reactions as well as to
fission, and was more general than
any that had previously been available
in reaction-rate theory. The new
formula gave considerable insight into
the rate of passage over the fission
barrier.

At this particular point it is inter-
esting to note the caution with which
Bohr adopted the formula. He would
come in every other day or so, and we
would go at it for perhaps a half a day,
trying out first this approach and then
that approach. But his supreme cau-
tion was most evident when we wanted
to interpret the number of levels ac-
cessible in the transition state. Today
that number is called “the number of
channels,” and we use it as a formula
to describe the channel-analysis theory
of fission rate. Also we apply similar
channel-analysis considerations to
other nuclear reactions. But at that
time the idea that each one of these
individual channels has in principle a
definite experimentally observable sig-
nificance was, for us, of dubious cer-
tainty. Still less did we appreciate,
until the later work of Aage Bohr, the
possibility that each individual chan-
nel would have its individual angular

distribution from which one could de-
termine the K values of that channel.
The cautious phrase that was used in
reference to that channel number ap-
pears in the following quotation: “It
should be remarked that the specific
quantum-mechanical effects which set
in at and below the critical fission
energy may even show their influence
to a certain extent above this energy
and produce slight oscillations in the
beginning of the yield curve, allowing,
possibly, a direct determination of the
number of channels.” Of course we
know how later on in the 1950’s these
variations were observed by Lamphere
and Green and others and how they
led to direct measurement of the chan-
nel number.

Bohr’s epiphany

The most important part of this Prince-
ton period happened when I was not
in direct touch with Bohr. One snowy
morning he was walking from the
Nassau Club to his office in Fine Hall.
As a consequence of a breakfast dis-
cussion with George Placzek, who was
deeply skeptical of these fission ideas,
Bohr began struggling with the prob-
lem of explaining the remarkable de-
pendence of fission cross section on
neutron energy. In the course of the
walk he concluded that slow-neutron
fission is caused by U233 and fast-
neutron fission by U238. By the time
he had arrived at Fine Hall and he and
I had gathered together with Placzek
and Rosenfeld, he was ready to sketch
out the whole idea on the blackboard.
There he displayed the concept that
U238 is not susceptible to division by
neutrons of thermal energy, nor is it
susceptible to- neutrons of intermediate
energy but only to neutrons with ener-
gies of a million electron volts or more.
Further, the fission observed at lower
energies occurs because U235 is pres-
ent and has a 1/v cross section for
capture. We already knew experi-
mentally that neutrons of intermediate
energy undergo resonance capture.
And, with the help of simple con-
siderations, we could show that the
resonance reaction of neutrons with
uranium could not be due to U233. We
concluded this because we knew that
the resonance cross section would ex-
ceed the theoretical limit given by the
square of the wavelength if U235 were

responsible for the resonance effect.
So the resonance had to be due to
U238, and the very fact that the reso-
nance neutrons did not bring about
fission proved that U238 was not sus-
ceptible to fission by neutrons of such
low energy. Thus if it was not sus-
septible at that energy, it would cer-
tainly not be susceptible at lower
energies; consequently low-energy fis-
sion must be due to U233.

Around this time, Szilard, Placzek,
Wigner, Rosenfeld, Bohr, myself and oth-
ers discussed whether one could ever
hope to make a nuclear explosive. It was
so preposterous then to think of separat-
ing U235 that I cannot forget the words
that Bohr used in speaking about it: “It
would take the entire efforts of a country
to make a bomb.” He did not foresee that,
in truth, the efforts of thousands of
workers drawn from three countries
would be needed to achieve that goal.

The theory of fission made it pos-
sible to predict in general terms how
the cross section for fission would de-
pend upon energy. In Palmer Physical
Laboratory Rudolf Ladenberg, James
Kanner, Heinz H. Barschall and Van
Voorhies, just at the time we were
working on the theory, actually mea-
sured the cross section of uranium in
the region from two million to three
million volts— and also the cross section
for thorium, all of which fitted in with
predictions. The same considerations
of course made it possible to predict
that plutonium 239 would be fissile.
For this application of the theory we
are especially indebted to Louis A.
Turner. One started on the way that
ultimately led to the giant plutonium
project having only this theoretical
estimate to light and encourage the first
steps.

Spontaneous fission offered a most
attractive application of these ideas in
conjunction with the concept of barrier
penetration. Another application dealt
with the difference between prompt
neutrons and delayed neutrons. In
conclusion, nuclear fission brought us a
process distinguished from all the
other processes with which we ever
dealt before in nuclear physics, in that
we have for the first time in fission a
nuclear transformation inescapably
collective in character. In this sense
fission opened the door to the develop-
ment of the collective model of the
nucleus in the postwar years. □

282

HISTORY OF PHYSICS

PHYSICS at

By Enrico Fermi

The following is a verbatim transcript of Enrico Fermi’s
last address before the American Physical Society, delivered
informally and without notes at Columbia University’s
McMillin Theater on Saturday morning, January 30, 1954.
His retiring presidential address was delivered one day
earlier. The present speech, transcribed from a tape record-
ing, is left deliberately in an unpolished and unedited form.
Such informality would no doubt have been frowned upon
by Fermi, who was very particular about his published
writings. For those who knew Fermi or heard him speak,
however, the verbatim transcript may serve (as no formal
document could ever serve) to bring back for a moment
the very sound of his voice. The paper was presented as
part of the session “Physics at Columbia University” during
the Society’s 1954 annual meeting.

ENRICO FERMI

Mr. Chairman, Dean Pegram, fellow members, ladies
and gentlemen:

IT seems fitting to remember, on this 200th anniver-
sary of Columbia University, the key role that the
University played in the early experimentation and the
organization of the early work that led to the devel-
opment of atomic energy.

I had the good fortune to be associated with the
Pupin Laboratories through the period of time when
at least the first phase of this development took place.
I had had some difficulties in Italy and I will always
be very grateful to Columbia University for having
offered me a position in the Department of Physics at
the most opportune moment. And in addition this offer
gave me, as I said, the rare opportunity of witnessing
the series of events to which I have referred.

In fact I remember very vividly the first month,
January, 1939, that I started working at the Pupin
Laboratories because things began happening very fast.
In that period, Niels Bohr was on a lecture engagement
in Princeton and I remember one afternoon Willis Lamb
came back very excited and said that Bohr had leaked
out great news. The great news that had leaked out
was the discovery of fission and at least an outline of
its interpretation; the discovery as you well remember
goes back to the work of Hahn and Strassmann and at
least the first idea for the interpretation came through
the work of Lise Meitner and Frisch who were at that
time in Sweden.

Ik

PERSONAL ACCOUNTS

283

COLUMBIA UNIVERSITY

the Genesis of the
Nuclear
Energy
Project

PHYSICS TODAY / NOVEMBER 1955

Then, somewhat later that same month, there was a
meeting in Washington organized by the Carnegie In-
stitution in conjunction with George Washington Uni-
versity where I took part with a number of people from
Columbia University and where the possible importance
of the new-discovered phenomenon of fission was first
discussed in semi-jocular earnest as a possible source
of nuclear power. Because it was conjectured, if there
is fission with a very serious upset of the nuclear struc-
ture, it is not improbable that some neutrons will be
evaporated. And if some neutrons are evaporated, then
they might be more than one; let’s say, for the sake of
argument, two. And if they are more than one, it may
be that the two of them, for example, may each one
cause a fission and from that one sees of course a be-
ginning of the chain reaction machinery.

So that was one of the things that was discussed at
that conference and started a small ripple of excitement
about the possibility of releasing nuclear energy. At the
same time experimentation was started feverishly in
many laboratories, including Pupin, and I remember
before leaving Washington I had a telegram from Dun-
ning announcing the success of an experiment directed
to the discovery of the fission fragments. The same ex-
periment apparently was at the same time carried out
in half a dozen places in this country and in three or
four, in fact I think slightly before, in three or four
places in Europe.

Now a rather long and laborious work was started at
Columbia University in order to firm up these vague
suggestions that had been made as to the possibilities
that neutrons were emitted and try to see whether neu-
trons were in fact emitted when fission took place and

if so how many they -would be, because clearly a matter
of numbers is in this case extremely important because
a little bit greater or a little bit lesser probability might
have made all the difference between possibility and
impossibility of a chain reaction.

Now this work was carried on at Columbia simul-
taneously by Zinn and Szilard on one hand and by
Anderson and myself on the other hand. We worked
independently and with different methods, but of course
we kept close contact and we kept each other informed
of the results. At the same time the same work was
being carried out in France by a group headed by Joliot
and Von Halban. And all the three groups arrived at
the same conclusion — I believe Joliot may be a few
weeks earlier than we did at Columbia — namely that
neutrons are emitted and they were rather abundant,
although the quantitative measurement was still very
uncertain and not too reliable.

A curious circumstance related to this phase of the
work was that here for the first time secrecy that has
been plaguing us for a number of years started and,
contrary to perhaps what is the most common belief
about secrecy, secrecy was not started by generals, was
not started by security officers, but was started by physi-
cists. And the man who is mostly responsible for this
certainly extremely novel idea for physicists was Szilard.

I don’t know how many of you know Szilard; no
doubt very many of you do. He is certainly a very
peculiar man, extremely intelligent (LAUGHTER). I
see that is an understatement (LAUGHTER). He is ex-
tremely brilliant and he seems somewhat to enjoy, at
least that is the impression that he gives to me, he
seems to enjoy startling people.

HISTORY OF PHYSICS

So he proceeded to startle physicists by proposing to
them that given the circumstances of the period — you
see it was early 1939 and war was very much in the
air — given the circumstances of that period, given the
danger that atomic energy and possibly atomic weapons
could become the chief tool for the Nazis to enslave
the world, it was the duty of the physicists to depart
from what had been the tradition of publishing signifi-
cant results as soon as the Physical Review or other
scientific journals might turn them out, and that in-
stead one had to go easy, keep back some results until
it was clear whether these results W'ere potentially dan-
gerous or potentially helpful to our side.

So Szilard talked to a number of people and con-
vinced them that they had to join some sort of — I don’t
know wdiether it would be called a secret society, or
what it would be called. Anyway to get together and
circulate this information privately among a rather re-
stricted group and not to publish it immediately.
He sent in this vein a number of cables to Joliot in
France, but he did not get a favorable response from
him and Joliot published his results more or less like
results in physics had been published until that day.
So that the fact that neutrons are emitted in fis-
sion in some abundance — the order of magnitude of one
or two or three — became a matter of general knowledge.
And, of course, that made the possibility of a chain re-
action appear to most physicists as a vastly more real
possibility than it had until that time.

Another important phase of the work that took place
at Columbia University is connected with the suggestion
on purely theoretical arguments, by Bohr and Wheeler,
that of the two isotopes of uranium it was not the most
abundant uranium 238 but it was the least abundant
uranium 23S, present as you know in the natural ura-
nium mixture to the tune of 0.7 of a per cent, that was
responsible at least for most of the thermal fission. The
argument had to do with an even number of neutrons
in uranium 238 and an odd number of neutrons in ura-
nium 235 which, according to a discussion of the bind-
ing energies that was carried out by Bohr and Wheeler,
made plausible that uranium 235 should be more fis-
sionable.

Now it clearly was very important to know the facts
also experimentally and work was started in conjunc-
tion by Dunning and Booth at Columbia University and
by Nier. Nier took the mass spectrographic part of this
work, attempting to separate a minute but as large as
possible amount of uranium 235, and Dunning and
Booth at Columbia took over the part of using this
minute amount in order to test whether or not it would
undergo fission with a much greater cross section than
ordinary uranium.

Well, you know of course by now that this experi-
ment confirmed the theoretical suggestion of Bohr and
Wheeler, indicating that the key isotope of uranium,
from the point of view of any attempt of — for example
— constructing a machine that would develop nuclear
energy, was in fact uranium 235. Now you see the mat-

ter is important primarily for the following reasons that
at the time were appreciated perhaps less definitely than
at the present moment.

The fundamental point in fabricating a chain reacting
machine is of course to see to it that each fission pro-
duces a certain number of neutrons and some of these
neutrons will again produce fission. If an original fis-
sion causes more than one subsequent fission then of
course the reaction goes. If an original fission causes
less than one subsequent fission then the reaction does
not go.

Now, if you take the isolated pure isotope U-235,
you may expect that the unavoidable losses of neutrons
will be minor, and therefore if in the fission somewhat
more than one neutron is emitted then it will be merely
a matter of piling up enough uranium 235 to obtain a
chain reacting structure. But if to each gram of ura-
nium 235 you add some 140 grams of uranium 238 that
come naturally with it, then the competition will be
greater, because there will be all this ballast ready to
snatch away the not too abundant neutrons that come
out in the fission and therefore it was clear at the time
that one of the ways to make possible the production
of a chain reaction was to isolate the isotope U-235
from the much more abundant isotope U-238.

Now, at present we have in our laboratories a row
of bottles labeled, more or less, isotope — what shall 1
say — iron 56, for example, or uranium 235 or uranium
238 and these bottles are not quite as common as would
be a row of bottles of chemical elements, but they are
perfectly easily obtainable by putting due pressure on
the Oak Ridge Laboratory (LAUGHTER). But at that
time isotopes were considered almost magically insep-
arable. There was to be sure one exception, namely
deuterium, which was already at that time available in
bottles. But of course deuterium is an isotope in which
the tw'O isotopes hydrogen one and hydrogen two have
a ratio of mass one to two, which is a very great ratio.
But in the case of uranium the ratio of mass is merely
235 to 238, so the difference is barely over one per cent.
And that, of course, makes the differences of these two
objects so tiny that it was not very clear that the job
of separating large amounts of uranium 235 was one
that could be taken seriously.

Well, therefore, in those early years near the end of
1939 two lines of attack to the problem of atomic en-
ergy started to emerge. One was as follows. The first
step should be to separate in large amounts, amounts
of kilograms or maybe amounts of tens of kilograms
or maybe of hundreds of kilograms, nobody really knew
how much would be needed, but something perhaps in
that order of magnitude, separate such at that time
fantastically large-looking amounts of uranium 235 and
then operate with them without the ballast of the
associated much larger amounts of uranium 238. The
other school of thought was predicated on the hope
that perhaps the neutrons would be a little bit more
and that perhaps using some little amount of ingenuity
one might use them efficiently and one might perhaps
be able to achieve a chain reaction without having to

PERSONAL ACCOUNTS

285

separate the isotopes, a task as I say that at that time
looked almost beyond human possibilities.

Now I personally had worked many years with neu-
trons, and especially slow neutrons, so I associated my-
self with the second team that wanted to use non-
separated uranium and try to do the best with it. Early
attempts and studies, discussions, on how to separate
the isotopes of uranium were started by Dunning and
Booth in close consultation with Professor Urey. On the
other hand, Szilard, Zinn, Anderson, and myself started
experimentation on the other line whose first step in-
volved lots of measurements.

Now, I have never yet quite understood why our
measurements in those days were so poor. I’m noticing
now that the measurements that we are doing on pion
physics are very poor, presumably just because we have
not learned the tricks. And, of course, the facilities that
we had at that time were not as powerful as they are
now. It’s much easier to carry out experimentation with
neutrons using a pile as a source of neutrons than it
was in those days using radium-beryllium sources when
geometry was the essential item to control or using the
cyclotron when intensity was the desired feature rather
than good geometry.

Well, we soon reached the conclusion that in order
to have any chance of success with natural uranium we
had to use slow neutrons. So there had to be a modera-
tor. And this moderator could have been first water or
other substances. Water was soon discarded; it’s very
effective in slowing down neutrons, but still absorbs a
little bit too many of them and we could not afford that.
Then it was thought that graphite might be perhaps the
better bet. It’s not as efficient as water in slowing down
neutrons; on the other hand little enough was known
of its absorption properties that the hope that the ab-
sorption might be very low was quite tenable.

This brings us to the fall of 1939 when Einstein wrote
his now famous letter to President Roosevelt advising
him of what was the situation in physics — what was
brewing and that he thought that the government had
the duty to take an interest and to help along this de-
velopment. And in fact help came along to the tune of
$6000 a few months after and the $6000 were used in
order to buy huge amounts — or what seemed at that
time when the eye of physicists had not yet been dis-
torted— (LAUGHTER) what seemed at that time a
huge amount of graphite.

So physicists on the seventh floor of Pupin Labora-
tories started looking like coal miners (LAUGHTER)
and the wives to whom these physicists came back
tired at night were wondering what was happening.
We know that there is smoke in the air, but after all
(LAUGHTER).

Well, what was happening was that in those days we
were trying to learn something about the absorption
properties of graphite, because perhaps graphite was
no good. So, we built columns of graphite, maybe four
feet on the side or something like that, maybe ten feet
high. It was the first time when apparatus in physics,
and these graphite columns were apparatus, was so big

that you could climb on top of it — and you had to
climb on top of it. Well, cyclotrons wrere the same way
too, but anyway the first time when I started climbing
on top of my equipment because it was just too tall —
Pm not a tall man (LAUGHTER).

And then sources of neutrons were inserted at the
bottom and we were studying how these neutrons were
first slowed down and then diffused up the column and
of course if there had been a strong absorption they
would not have diffused very high. But because it
turned out that the absorption was in fact small, they
could diffuse quite readily up this column and by
making a little bit of mathematical analysis of the
situation it became possible to make the first guesses
as to what was the absorption cross section of graphite,
a key element in deciding the possibility or not of fab-
ricating a chain reacting unit with graphite and natural
uranium.

Well, I will not go into detail of this experimentation.
That lasted really quite a number of years and required
really quite many hours and many days and many weeks
of extremely hard work. I may mention that very early
our efforts were brought in connection with similar ef-
forts that were taking place at Princeton University
where a group with Wigner, Creutz and Bob Wilson set
to work making some measurements that we had no
possibility of carrying out at Columbia University.

Well, as time went on, we began to identify what had
to be measured and how accurately these things that I
shall call “eta”, /, and p — I don’t think I have time to
define them for you — these three quantities “eta”, /, and
p had to be measured to establish what could be done
and what could not be done. And, in fact, if I may say
so, the product of “eta”, /, and p had to be greater than
one. It turns out, we now know, that if one does just
about the best this product can be 1.1.

So, if we had been able to measure these three quan-
tities to the accuracy of one per cent we might have
found that the product was for example 1.08 plus or
minus 0.03 and if that had been the case we would have
said let’s go ahead, or if the product had turned out to
be 0.9S plus or minus 0.03 perhaps we would have said
just that this line of approach is not very promising,
and we had better look for something else. However
I’ve already commented on the extremely low quality
of the measurements in neutron physics that could be
done at the time — where the accuracy of measuring sep-
arately either “eta”, or /, or p was perhaps with a plus
or minus of 20 per cent (LAUGHTER). If you com-
pound, by the well-known rules of statistics, three errors
of 20 per cent you will find something around 35 per
cent. So if you should find, for example, 0.9 plus or
minus 0.3 — what do you know? Hardly anything at all
(LAUGHTER). If you find 1.1 plus or minus 0.3 —
again, you don’t know anything much. So that was the
trouble and in fact if you look in our early work —
what were the detailed values given by this or that ex-
perimenter to, for example, “eta” you find that it was
off 20 per cent and sometimes greater amounts. In fact
I think it was strongly influenced by the temperament

HISTORY OF PHYSICS

of the physicist. Shall we say optimistic physicists felt
it unavoidable to push these quantities high and pes-
simistic physicists like myself tried to keep them some-
what on the low side (LAUGHTER).

Anyway, nobody really knew and we decided there-
fore that one had to do something else. One had to
devise some kind of experiment that would give a
complete over-all measurement directly of the product
“eta”, /, p without having to measure separately the
three, because then perhaps the error would sort of
drop down and permit us to reach conclusions.

Well, we went to Dean Pegram, who was then the
man who could carry out magic around the University,
and we explained to him that we needed a big room.
And when we say big we meant a really big room,
perhaps he made a crack about a church not being the
most suited place for a physics laboratory in his talk,
but I think a church would have been just precisely
what we wanted (LAUGHTER). Well, he scouted
around the campus and we went with him to dark cor-
ridors and under various heating pipes and so on to visit
possible sites for this experiment and eventually a big
room, not a church, but something that might have
been compared in size with a church was discovered in
Schermerhorn.

And there we started to construct this structure that
at that time looked again in order of magnitude larger
than anything that we had seen before. Actually if
anybody would look at that structure now he would
probably extract his magnifying glass (LAUGHTER)
and go close to see it. But for the ideas of the time
it looked really big. It was a structure of graphite bricks
and spread through these graphite bricks in some sort
of pattern were big cans, cubic cans, containing uranium
oxide.

Now, graphite is a black substance, as you probably
know. So is uranium oxide. And to handle many tons
of both makes people very black. In fact it requires
even strong people. And so, well we were reasonably
strong, but I mean we were, after all, thinkers (LAUGH-
TER). So Dean Pegram again looked around and said
that seems to be a job a little bit beyond your feeble
strength, but there is a football squad at Columbia
(LAUGHTER) that contains a dozen or so of very
husky boys who take jobs by the hour just to carry
them through College. Why don’t you hire them?

And it was a marvelous idea; it was really a pleasure
for once to direct the work of these husky boys, canning
uranium — just shoving it in — handling packs of 50 or
100 pounds with the same ease as another person would
have handled three or four pounds. In passing these
cans fumes of all sorts of colors, mostly black, would
go in the air (LAUGHTER).

Well, so grew what was called at the time the ex-
ponential pile. It was an exponential pile, because in
the theory an exponential function enters — which is
not surprising. And it was a structure that was designed
to test in an integral way, without going down to fine
details, whether the reactivity of the pile, the repro-
duction factor, would be greater or less than one. Well,

it turned out to be 0.87. Now that is by 0.13 less than
one and it was bad. However, at the moment we had a
firm point to start from, and we had essentially to see
whether we could squeeze the extra 0.13 or preferably
a little bit more. Now there were many obvious things
that could be done. First of all, I told you these big
cans were canned in tin cans, so what has the iron to
do? Iron can do only harm, can absorb neutrons, and
we don’t want that. So, out go the cans. Then, what
about the purity of the materials? We took samples of
uranium, and with our physicists’ lack of skill in chem-
ical analysis, we sort of tried to find out the impurities
and certainly there were impurities. We would not know
what they were, but they looked impressive, at least
in bulk (LAUGHTER). So, now, what do these impu-
rities do? — clearly they can do only harm. Maybe they
make harm to the tune of 13 per cent. Finally, the
graphite was quite pure for the standards of that time,
when graphite manufacturers were not concerned with
avoiding those special impurities that absorb neutrons.
But still there was some considerable gain to be made
out there, and especially Szilard at that time took ex-
tremely decisive and strong steps to try to organize the
early phases of production of pure materials. Now, he
did a marvelous job which later on was taken over by
a more powerful organization than was Szilard himself.
Although to match Szilard it takes a few able-bodied
customers (LAUGHTER).

Well, this brings us to Pearl Harbor. At that time,
in fact I believe a few days before by accident, the in-
terest in carrying through the uranium work was spread-
ing; work somewhat similar to what was going on at
Columbia had been initiated in a number of different
Universities throughout the country. And the govern-
ment started taking decisive action in order to organize
the work, and, of course, Pearl Harbor gave the final
and very decisive impetus to this organization. And it
was decided in the high councils of the government that
the work on the chain reaction produced by nonsepa-
rated isotopes of uranium should go to Chicago.

That is the time when I left Columbia University,
and after a few months of commuting between Chicago
and New York eventually moved to Chicago to keep
up the work there, and from then on, with a few no-
table exceptions, the work at Columbia was concen-
trated on the isotope-separation phase of the atomic
energy project.

As I’ve indicated this work was initiated by Booth,
Dunning, and Urey about 1940, 1939, and 1940, and
with this reorganization a large laboratory was started
at Columbia under the direction of Professor Urey.
The work there was extremely successful and rapidly
expanded into the build-up of a huge research labora-
tory which cooperated with the Union Carbide Com-
pany in establishing some of the separation plants at
Oak Ridge. This was one of the three horses on which
the directors of the atomic energy project had placed
their bets, and as you know the three horses arrived
almost simultaneously to the goal in the summer of
1945. I thank you. (APPLAUSE)

287

^—Chapter 6 .
Particles and Quanta

rp he physics of atoms, quanta, and elementary particles
has caught the attention of more historians than any
other field of modern science. At no time were more than a
minority of physicists working in this area, but the area has
had an unmatched impact on all of science and even on
philosophy. Quantum mechanics in particular, by way of
chemical physics, condensed matter physics, and so forth,
has been at the center not only of a revolution in thought
but of a new industrial era. Study of the history of the area
has been accordingly extensive, indeed so extensive that we
can give it, alone among the subfields of physics, a separate
section of this book. As usual the articles are arranged
roughly in chronological order.

The section begins with the discovery of the electron,
which was the first true elementary particle to be
identified, and also the key to atomic physics, and also
ultimately the key to understanding quanta. Contrary to a
myth that is still widespread, few physicists prior to the
time of that discovery saw their field as moribund; most put
their faith in exciting and ambitious programs to get at the
mysterious heart of matter and energy. Many physicists
were motivated by a confusion of electromagnetic theories
which seem peculiar today, but which convinced them that
great secrets lay near the surface, and it was this
intellectual ferment that produced the discoveries of
Rontgen, Becquerel, Thomson, and Planck. But the
discoveries were even more astonishing than they had

anticipated. The next several decades were a turmoil of
misunderstandings and incredible ideas. After the late
1930s with the coming of nuclear physics, field theory, and
a distinct physics of elementary particles, things settled
down into a new intellectual configuration, whose basic
outlines have stayed intact down to the present.

Among the articles here, those by Thomson, Condon,
Bloch, Schmitt, and Weisskopf are written by scientists
who witnessed or came close to witnessing the events they
describe. These articles thus have some of the advantages,
and pitfalls, of first-person accounts, as discussed in the
introduction to the previous section. However, the
physicists in this section are not so much describing their
own work as the work that was going on around them. Such
descriptions, whether relatively informal accounts of the
sort reprinted here, or highly stylized review articles, are
the traditional starting-point for work by professional
historians. The remaining articles in this section are
written by some of our foremost professional historians of
physics. Note that these historians approach the subject
from a quite different viewpoint than the physicists,
typically less personal and more analytic. It is such a
mixture of two viewpoints, the original scientists’
experiences and the subsequent interpretation by
historical scholarship, that gives history of modern physics
its tremendous vigor and appeal.

289

294

303

310

319

324

332

340

346

354

358

Contents

J. J. Thomson and the discovery of the electron . .
Thermodynamics and quanta in Planck’s work . . .

J. J. Thomson and the Bohr atom

Sixty years of quantum physics

Heisenberg and the early days of quantum mechanics

Electron diffraction: Fifty years ago

1932 — Moving into the new physics

The idea of the neutrino

The birth of elementary-particle physics

The discovery of electron tunneling into superconductors
The development of field theory in the last fifty years .

George P. Thomson
Martin J. Klein
John L. Heilbron
Edward U. Condon
Felix Bloch

Richard K. Gehrenbeck
Charles Weiner
Laurie M. Brown
Laurie M. Brown and

Lillian Hartmann Hoddeson
Roland W. Schmitt
Victor F. Weisskopf

PARTICLES AND QUANTA

289

J. J. THOMSON

and the discovery of the Electron

PHYSICS TODAY / AUGUST 1956

By George P. Thomson

Conference members (from
left to right) L. B. Leder, L.
Marton, H. S. W. Massey, G.
P. Thomson, F. L. Hereford,
A. Klein, R. D. Birkhoff, A. W.
Kenney, H. A. Tolhoek.

Sir George P. Thomson, FRS (right), is Master of Corpus
Christi College, Cambridge, England. The son of Sir. J. J.
Thomson, Sir George shared the 1937 Nobel Prize in
physics with C. J. Davisson for the discovery of the dif-
fraction of electrons by crystals. The present paper is the
text of his after-dinner address at the Electron Physics
Conference Banquet.

MAY I say that I am particularly glad and happy
that my father’s hundredth anniversary of his
birth should be celebrated here in this way. My father
had a great affection for America at all times, and of
all the places in America, he best knew and loved Balti-
more; and that it should be the University of Mary-
land which is honouring him in this way is to me a
very great pleasure, as it would have been to him.

Now, I have to speak not only of J. J. but also of
the discovery of the electron; and the electron was, as

most people know, named before it was discovered, and
the anomaly that this implies has its counterpart in an
uncertainty of meaning which I think to some extent
still subsists. The two parent strains from which the
electron sprang have not even now completely fused,
and indeed it was the blending of two different trains
of thought which constituted its discovery. They are,
first, the idea of a natural unit of electric charge, and
second, the existence of very light electrified particles
fundamental in the structure of matter. The first is

290

HISTORY OF PHYSICS

The following impressions are those of
Lord Rutherford after having visited
J. J. Thomson, Mrs. Thomson, and the
young George Thomson:

“Cambridge: 3 Oct. 1895. . . . Next
day I had an appointment to go and
see Thomson at Cambridge. . . . I went
to the Lab and saw Thomson and had
a good long talk with him. He is very
pleasant in conversation and is not fos-
silized at all. As regards appearance he
is a medium sized man, dark and quite
youthful still: Shaves, very badly, and
wears his hair rather long. His face is
rather long and thin; has a good head
and has a couple of vertical furrows
just above his nose. . . . He asked me
up to lunch to Scroope Terrace where
l saw his wife, a tall, dark woman.

/ have forgotten to mention the great
things 1 saw — the only boy of the
house — 3i years old — a sturdy young-
ster of Saxon appearance but the best
little kid 1 have seen for looks and
size. Prof. J. J. is very fond of him
and played about with him during
lunch while Mrs. J. J. apologised for
the informality . I like Mr. and Mrs.
both very much. . .

From a letter by Rutherford to Mary Newton

Sir Joseph J. Thomson

inherent, in the work of Faraday on electrolysis, and it
is to me one of the most curious features of the his-
tory of physics that it should have taken people so long
to realise that Faraday’s laws of electrolysis are only
intelligible if you suppose that there is a fundamental
unit of charge involved. But in fact it seems to have
taken a long time for people to do so. Johnstone Stoney
in 1874 called attention to the importance of the charge
carried by the hydrogen ion in electrolysis, and in the
early 80s he estimated its value; I may say he got it
16 times too small, but he named it the electron in 1891.

There were electron theories in the course of the
19th century, but they were not very important. It was
not until the great theory of Lorentz in the early 90’s
which predicted the effect that Zeeman found in ’96.
that electrons became important in theoretical physics.
But since I am speaking in commemoration of the 100th
anniversary of the birth of J. J., I will leave that side
of the picture and turn to the side with which he was
personally concerned. But I should like first to say a
few words about his background.

He was, as you have been told, born 100 years ago.
He was a son of a Manchester book-seller and publisher
who died when he was 16, and there is little recorded
about his boyhood. He was given at some suitable age
a microscope, and I would like to say of course that

Sir George P. Thomson

PARTICLES AND QUANTA

291

that turned his thoughts to science and was the begin-
ning of his career. I do not think it was. but there is a
story about it which I might as w'ell tell you.

He got the microscope and examined things in it. A
friend of his father’s came along one day and to show
it off he put a hair, a human hair, presumably one of
his own because he had no sisters to pull hairs out of,
on the stage, focussed it duly, and asked the father’s
friend to look. He looked and seemed puzzled. J. J.
said “Can’t you see it?’’

“Oh. yes, 1 can see it all right’’, said the friend, “but
where is the number?"

“Number?" asked J. J.

“Yes, you know, it’s in the Bible. All the hairs of
your head are numbered.”

My father’s original ambition was to be an engineer
and I think it is probable that if his father had lived he
w'ould have been. In those days in order to become an
engineer you had to be taken on by a firm in a kind of
quasi-apprenticeship and pay a very substantial pre-
mium for the privilege. The family w'as not rich enough
to afford this, but J. J. went, at a very early age, to
what was then called Owens College and is now the
University of Manchester. He was trained there as a
mathematician and at 19 he went to Cambridge with a
scholarship to Trinity College, of which he was master
for the last 22 years of his life. After he had taken his
mathematical degree he worked in the Cavendish Labo-
ratory under Lord Rayleigh w'ho was professor for a
not very long time, in succession to Maxwell. His early
theoretical w'ork was really inspired by Maxwell’s the-
ory. It is perhaps difficult for us who have had to face
so many worse things, to realise that in these early days
Maxwell's theory was regarded as the limit of obscurity.
Actually, if you read Maxwell, you will see that there
was something to be said for this view. He was not
very skilful, perhaps, in putting forward what he was
thinking about and it is expressed in a rather curious
fashion. The displacement, for example, which figures
so largely in it : it is not really clear precisely how
Maxw'ell did in fact envisage it, and it must have been
a very difficult idea for his contemporaries.

My father published an edition of Maxwell’s theory
and supplemented it by a volume called “Recent Re-
searches" which were really a kind of commentary on
it and the working out of a number of problems sug-
gested by it. He discovered, if “discovered" is the right
word (predicted the existence of is perhaps better),
electromagnetic mass, the first example of the connec-
tion of mass with energy. That was in the year 1881.
About this time he was attracted by a theory which I
suppose few people have even heard of, and that is
Helmholtz’s vortex theory of atoms, a theory based on
vortex rings presumed to exist in the ether, and ca-
pable of the most delightful mathematical complexities
as they interlocked and performed curious gyrations
round one another. It is interesting in its way as a
theory of matter which is almost purely kinematic: dy-
namics hardly comes into it; it is the motion produced
by each vortex in the other vortices, you see, which

governs the w'hole thing. J. J. published a long prize
essay on it, but the most important point, from our
point of view tonight, is that it first called his atten-
tion to the gaseous discharge. He thought that it was
possible that what happened in the gaseous discharge
was that molecules of two atoms each were pulled
apart, and by the theory it was reasonable to guess that
this might produce electrification. Anyhow he started
experiments on the gaseous discharge in 1886 and for
about 50 years afterwards he was rarely, if ever, with-
out some work on gaseous discharge in one form or
another on hand. He was always fascinated with it and
indeed I think those who have worked in that field, as
most of us here perhaps have done, recognize the fasci-
nation. But in fact no great advance was made until
Roentgen’s discovery of x-rays in 1895. This was cer-
tainly one of the major things in physics, quite com-
parable with Galvani’s discovery of the twitching frog’s
leg, and it gave the same kind of thrill to its age that
the discovery of nuclear fission gave to ours.

I would like just to tell a very short story that is
not very relevant but it is of interest to physicists as
to how, if you wash, you can avoid making discoveries.

At the time that Roentgen was working with the dis-
charge tube, other people were also. And one of them,
who shall be nameless, he was not a very famous physi-
cist, discovered that photographic plates, when near
this tube, got fogged. Well, he was intent on the job
he was doing, and he was a man of common sense, so
he took the plates further away.

Rutherford had only recently come to Cambridge
from New Zealand. His work there had been on the
electromagnetic waves, and he was a pioneer in what
we in England call “wireless” and you call radio. He
continued this work for a little while at Cambridge.
But this discovery of x-rays called him to atomic phys-
ics, and he moved on to create nuclear physics.

J. J. turned to the line which led to the discovery of
the electron, namely cathode rays. Cathode rays had
been known for about 50 years, but there was at the
time a great controversy as to their nature, a contro-
versy which was of an international character for the
two sides were, in a sense, divided by the Rhine. The
Germans held the view that these cathode rays were in
their nature waves; the French and the British for the
most part held that they W'ere particles. Lenard had
shown that they could emerge from the exhausted tube
into the air and appear as a visible streak of luminosity.
They could emerge through thin but appreciable thick-
nesses of solid metal. Now to people in those days it
seemed quite inconceivable that any material particle
could get through metal and go on in something like
the same straight line. It was a very strong argument
in favour of some kind of wave motion. Perrin, on the
other hand, had shown that when received in a Faraday
cylinder they gave it an electric charge. I’m not so sure
whether that would be quite such a strong argument
now-a-days — we should think rather of the possibilities
of secondaries. He also showed that when the cathode
rays were deflected away by a magnet the charge ceased.

HISTORY OF PHYSICS

One of my father’s first experiments in this field was to
carry Perrin’s one stage further to show that when the
Faraday cylinder was not in line with the original rays
it did not receive a charge, but that the charge appeared
when they were bent by a magnet so that their path as
shown by their luminosity made them hit the cylinder.

But a more fundamental attack was the attempt to
measure the ratio of the charge to the mass. Many at-
tempts at measuring this and so comparing it with the
same ratio for the ions in electrolysis were made in the
year 1897. Now, of course, from the knowledge of the
stiffness in a magnetic field, it was easy to find e/mv.
But you had to find something else, either v or per-
haps \mv-. A number of these attempts were made.
Some, I think, were based on unjustifiable assumptions,
but one, at least (that due to Wiechert which was pub-
lished in January 1897), was quite sound in principle.
It attempted to measure v by comparing the time that
the cathode rays took to go a certain distance with the
time of oscillation of an electrical circuit. But, in fact,
in his early experiments Wiechert did not make a meas-
urement, he only got a lower limit and he only did it
x for one gas. J. J. always stressed the importance of the
constancy of e/m for different gases and different elec-
trodes; and in February of that same year he showed
that mv/e} that is to say the stiffness of the rays, was
the same for all gases provided the voltage was con-
stant. My father s first measurement of e/ m appeared
in a lecture at the Royal Institution of London on the
30th of April 1897 and was published a fortnight later
in The Electrician. In this first measurement he used a
thermopile and a Faraday cylinder to measure the total
energy in a given time and also the charge; that is, he
measured effectively e/mv- for the individual particle,
and then, having e/mv from the magnetic deflection,
of course both e/m and v followed. This led to the re-
sult that e/m was' about a thousand times that for the
ion of hydrogen.

Then came the better known method using the elec-
trostatic deflection, the origin of the cathode ray oscil-
lograph. And this perhaps was most important, not so
much for its actual measurement as for its accounting
for what was the strongest argument against the par-
ticle nature of the cathode rays — a piece of work by
Hertz who had tried to deflect them by electrostatic
action and had failed. Well, of course, we now know
that the reason that he failed was because the vacuum
wasn’t good enough. The gas between the plates be-
tween which the field was supposed to be applied was
ionized. The ions would flow towards the two plates
and virtually neutralize the field between them. By
slightly improving the vacuum (I don’t think it was
more than slightly improving, seeing what vacua were
like in those days and indeed much later) my father
was able to get it good enough so that he got the de-
flection, which indeed was an essential part of the
measurement.

In his earlier papers J. J. emphasized not merely the
large value of e/m but the fact that these corpuscles,
as he liked to call them, were a universal constituent of

matter, that they were the same whatever the gas in
the tube — he tried 4 I think, and whatever the metal
of which the electrodes were made, of which he tried 3.
Then followed a measurement of the charge e for the
x-ray ions which he had discovered a couple of years
before. It followed the now well-known method, due
to C. T. R. Wilson’s work on the condensation of
clouds on ions, work which incidentally was a conse-
quence of the theory my father had developed earlier,
on the connection between energy, and chemical and
physical reactions. The charge was about the same as
for a monovalent ion. indicating that m for a cathode
ray was a thousand times less than for a hydrogen
atom.

This, in a sense, was not conclusive because there
was no absolute reason to suppose that the x-ray ions
had got anything very particular to do with the cathode
rays; one could not assert dogmatically that the charge
on the cathode ray was the same as the charge on the
negative x-ray ion, though most people thought it was.
Nevertheless, the proof was completed in 1899 by the
measurement simultaneously of e/m and e for the
photoelectric particles, which are now called photoelec-
tric electrons. This showed that he had found some-
thing very much smaller, at least a thousand times
smaller, than the mass of a hydrogen atom, and some-
thing, and this was much more important, something
which was a universal constituent of all matter. After
that no reasonable person could really refuse belief
that there were particles smaller than atoms, or lighter
than atoms at least, and that these particles played a
fundamental part in the constitution of matter.

I have no time in an after-dinner speech to speak of
his work on the electron theory of metals, or his theory
of atoms in which the electrons were supposed to be
imbedded in a uniform distribution of positive elec-
tricity, except perhaps to give the reason why he held
what now seems to be this rather odd idea. He did so
because he knew from the Newtonian theory that the
other obvious explanation, something like a solar sys-
tem, would be unstable. A solar system in which the
planets repel one another can be shown to be inher-
ently unstable. And unfortunately my father knew
that, for he was a very good mathematician. Nor will
I speak of his estimates by three methods of the num-
ber of electrons in the atoms of various elements which
led to the conclusion that this number was not very
different from half the atomic weight. His very impor-
tant work on positive rays does not, I suppose, really
come under this subject, but it did of course lead to
the discovery of nonradioactive isotopes and was in-
deed, and this is perhaps not always realised, the first
experimental proof that atoms of any one substance
are equal in mass apart from isotopes, and that the
atomic weight is not merely a statistical property which
might really represent a continuous spread over a very
wide range. Before those experiments there was no real
evidence to show that that was not the case.

I should like to conclude, if I may, by saying a few
words about my father as a thinker and a man. His

PARTICLES AND QUANTA

character was in some ways rather anomalous. He was
a mathematician, a very good mathematician, who yet
liked his theories concrete. All his life he was attracted
by the idea of tubes of force, Faraday’s tubes of force,
and always tried to ascribe to them some kind of actual
physical reality. He liked something he could picture
and he entirely distrusted metaphysics. He preferred
the wave atom, the wave atom with the wave electron,
to the Bohr atom, at least as long as the waves could
be allowed to remain pictorial. He was a great experi-
mentalist who was liable to break any apparatus he
got near. He was singularly clumsy with his hands and
my mother, who was good at that kind of thing, never
dreamed of allowing him to knock a nail in.

He had most of the actual preparing of the experi-
ments done by his personal assistant Everett ; my father
just took the readings, which very often took the form
of examining a photographic record, for example of
positive rays, which he would measure. But he had an
uncanny power of diagnosing the reasons why appa-
ratus, his own or other people’s, would not work, and
suggesting what had to be done to make it work. He
was a man who was normally silent, but he was a witty

and amusing host at any sort of party, including the
daily teas held in his room in the Cavendish, which he
introduced. He loved flowers, wild and cultivated, and
knew a very great deal about them, but he seldom
gardened. He was fond of watching cricket, tennis, and
football, and could recall the names and achievements
of most of the leading people at Cambridge for the last
30 or 40 years in those sports. But in fact he had
played little himself. He was a man of exceptionally
wide sympathies. He could enjoy talking to almost any-
body, and had the knack of making other people talk
well about their own particular subject. He founded,
and these sympathies helped him to found, the first
school of physics, in a modem sense, at least outside
Germany, and at one time his pupils, Cavendish men,
held a very large fraction of the professorships through-
out the world. Though he had a strong sense of humour,
physics was too important to be funny, certainly too
important to be laughed at. For him the two great
qualities of a physicist, the two that really mattered,
were originality and enthusiasm; and though he rated
originality extremely high, it was enthusiasm which
stood at the top.

294

HISTORY OF PHYSICS

Thermodynamics and
Quanta in Planck’s Work

Planck’s search lor a deeper understanding of the second law of thermody-
namics led him to a strange and unexpected result— the concept of energy
quanta. His conservative attitude toward this revolutionary discovery expressed
itself in his attempts to reconcile the quantum with classical electrodynamics.

PHYSICS TODAY / NOVEMBER 1966

by Martin J. Klein

In January 1910 Max Planck sent a
paper to Annalen dar Physik on the
theory of black-body radiation.1 It was
his first paper on this subject since the
epoch-making work in which he had
introduced the concept of energy
quanta almost a decade earlier.
Planck had no new results to report,
but he felt that it was time he ex-
pressed his views on what had been
going on in the intervening years.
Not that there was so very much to
discuss: neither the problems of radi-
ation nor Planck’s startling idea that
energy could sometimes vary only in
discrete steps had yet seriously caught
the attention of most of his colleagues.
Planck himself, of course, had thought
a great deal about these things, as he
remarked in a letter to Walther
Nernst a few months later:2 “I can
say without exaggeration that for ten
years, without interruption, nothing
in physics has so stimulated me, agi-
tated me, and excited me as these

quanta of action.” But his approach
to the problems did not coincide with
those of the relatively few others who
had concerned themselves with the
theory of radiation, and Planck wanted
to point out the path that he consid-
ered most sensible and most promis-
ing for future success.

fn his paper, Planck arranged the
current views on radiation into a spec-
trum, placing his own in the solid cen-
tral position. The extreme right wing,
represented by James Jeans, was still
trying to maintain the soundness of
Hamilton’s equations and the cqui-
partition theorem. The fact that the
equipartition theorem could not ac-
count for the existence of the equi-
librium distribution of black-body ra-
diation, much less for its observed
form, had to be explained, according
to Jeans, by the absence of true ther-
modynamic equilibrium in the radia-
tion. At the opposite end of the spec-
trum of opinion were the radicals who

interpreted the failure of the equipar-
tition theorem as a sign that nine-
teenth-century physics, for all its great
successes, now needed sweeping
changes. The most daring of their pro-
posals suggested that radiation be con-
sidered as a collection of independent
particles of energy— light quanta—
rather than as continuous electromag-
netic waves. This position was ad-
vanced most forcefully by Albert Ein-
stein, who supported it with a variety
of arguments, drawing upon his un-

Martin J. Klein,
who is acting head
of the Physics De-
partment at Case
Institute of Tech-
nology, received
his Ph.D. at MIT
in 1948. He is edi-
tor of Collected
Scientific Papers of
Paid Ehrenfest and
has written extensively on the early his-
tory of the quantum theory.

PARTICLES AND QUANTA

295

PLANCK

matched insight into statistical me-
chanics.

Planck could not accept either of
these extreme viewpoints. Jeans’ at-
tempts to salvage the equipartition
theorem left him unconvinced. Some-
thing in classical physics had to be
given up. To that extent he could
agree with the radicals, but only to
that extent. For he was concerned that
they wanted to throw out too much.
He would not grant the cogency of
the arguments for a new corpuscular
theory of light, even though Einstein
claimed that his light quanta were a
necessary consequence of the observed
form of the black-body radiation law.
Planck was not ready to give up the
whole development from Huygens to
Maxwell and Hertz which had estab-
lished the electromagnetic wave theory
of light, “all those achievements
which belong to the proudest suc-
cesses of physics, of all science,” for
the sake of what he called a few highly
controversial arguments.

He was, however, ready to sacrifice
the equations of mechanics, and stated
his assurance that Hamilton’s equa-
tions could no longer be taken as gen-
erally valid. In that way the equipar-
tition theorem and its unfortunate
consequences could be avoided.

Planck was sure of something else:
The discontinuity expressed by his
quantum of action was real and would
have to be reckoned with. He foresaw
a future theory that would somehow
reconcile the existence of the quantum
of action with electrodynamics, but in
the meantime he advocated caution:
“One should proceed as conservatively
as possible in introducing the quan-
tum of action into the theory, making
only those changes in existing theory
that hate proved to be absolutely nec-
essary.”

Planck’s stand amounted to this:
He had no doubts about the funda-
mental importance of the quantum
of action itself, but he saw no need for
a real quantum theory of radiation
and matter of the kind that already
seemed inevitable to Einstein. I think
that this statement of Planck’s views
helps one to understand his work dur-
ing the next few years, in which he
seemed to retreat steadily from his
own radical step in 1900. I shall dis-
cuss some of this work later on in
this paper, but I want first to go back
and try to point out the way in which
the development of Planck’s ideas had
led him to adopt this attitude towards
the quantum and the quantum theory.

Second law as absolute

In his later years Planck often ex-
pressed his deep conviction that “the
search for the absolute” was “the
loftiest goal of all scientific activity.”3
The context of his remarks clearly in-
dicated that he saw the two laws of
thermodynamics as a prototype of that
“loftiest goal.” For Planck had formed
himself as a physicist by his self-study
of the writings of Rudolf Clausius, that
lucid but rather argumentative man
who first distinguished and formulated
the two laws of thermodynamics, and
it was thermodynamics as seen by
Clausius that set the pattern of
Planck’s scientific career. He devoted
the first fifteen years or so of that
career to clarifying, expounding and
applying the second law of thermo-
dynamics and especially the concept of
irreversibility. Planck’s solid and suc-
cessful work in this field did not bring
him all the satisfaction he might prop-
erly have expected. One reason was
that he learned, too late, that some of
his results had been anticipated a few

years earlier in the memoirs of Wil-
lard Gibbs. More disturbing was the
rise of a powerful school of thought,
the "Energeticists,” led by Wilhelm
Ostwald and Georg Helm, which re-
jected the clear distinctions made by
Clausius, and offered a new master-
theory that would have replaced the
elegant mathematical structure of
thermodynamics by a confused and in-
consistent tangle.4 Planck later de-
scribed his failure to persuade the
Energeticists of the errors of their
ways as “one of the most painful ex-
periences of my entire scientific life.”

As a disciple of Clausius, Planck
looked upon the second law of thermo-
dynamics as having absolute validity:
Processes in which the total entropy
decreased were to be strictly excluded
from the natural world. He did not
care to follow Clausius in pursuing
“the nature of motion which we call
heat,” or in searching for a mechani-
cal explanation of the second law of
thermodynamics.5 And he most cer-
tainly did not follow Ludwig Boltz-
mann in his reformulation of the sec-
ond law of thermodynamics as a sta-
tistical law. Boltzmann’s statistical me-
chanics made the increase of entropy
into a highly probable rather than an
absolutely certain feature of natural
processes, and this was not in keeping
with Planck’s own commitments. The
statistical interpretation of entropy is
conspicuously absent from the papers
Planck wrote in the early 1890’s under
such titles as “General Remarks on
Modern Developments in the Theory
of Heat”8 and “The Essence of the
Second Law of Thermodynamics.”7

One should not think, however, that
Planck was content to keep thermo-
dynamics a completely independent
subject, separate from the rest of phys-
ics. He preferred the rigorous argu-
ments of pure thermodynamics to the
difficult but approximate treatment
of molecular models in kinetic theory,
but he also felt strongly the need to
relate the irreversibility described by
the second law to the other funda-
mental laws governing the basic con-
servative processes. He rejected Boltz-
mann’s approach because it rested on
statistical assumptions, and Planck
wanted to avoid these. He hoped that
the principle of increasing entropy
could be preserved intact as a rigorous

296

HISTORY OF PHYSICS

theorem in some more comprehensive
and more fundamental theory.

Second law and Wien distribution
In March 1895 Planck presented a
paper to the Academy of Sciences at
Berlin that seemed to represent a basic
shift in his interests.8 He had just put
aside his usual thermodynamic con-
cerns to discuss the problem of the
resonant scattering of plane electro-
magnetic waves by an oscillating di-
pole of dimensions small compared
to the wave length. A careful reader
would have noticed, however, that at
the end of the paper Planck admitted
that this study was only undertaken
as a preliminary to tackling the prob-
lem of black-body radiation. The scat-
tering process offered a way of under-
standing how the equilibrium state of
the radiation in an enclosure at fixed
temperature could be maintained.
The thermodynamics of radiation was
the underlying problem, and Planck’s
attention may have been drawn to it
by Wien’s paper of 1894 which pre-
sented the displacement law.9

The following February Planck had
further results to report to the Acad-
emy.10 He had extended his studies
to the radiation damping of his
charged oscillators, and he was im-
pressed by the difference between ra-
diation damping and damping bv
means of the ordinary resistance of
the oscillator. Radiation damping was
a completely conservative mechanism
that did not require one to invoke
the transformation of energy into
heat, or to supply another character-
istic constant of the oscillator in order
to describe its damping. Planck
thought this could have far-reaching
implications for this fundamental
question of irreversibility and the sec-
ond law. As he put it, “The study of
conservative damping seems to me to
be of great importance, since it opens
up the prospect of a possible general
explanation of irreversible processes
by means of conservative forces— a
problem that confronts research in
theoretical physics more urgently
every day.”

One year later, in February 1897,
he communicated the first of what
would become a series of five papers,
extending over a period of more than
two years, on irreversible phenomena

HERTZ

in radiation.11 The extended intro-
duction itself indicated that Planck
was planning a major work. He began
by asserting that no one had yet suc-
cessfully explained how a system gov-
erned by conservative interactions
could proceed irreversibly to a final
state of thermodynamic equilibrium.
He explicitly discounted Boltzmann’s
H-theorem as an unsuccessful attempt
in this direction, citing the criticisms
recently raised by E. Zermelo, Planck’s
own student, against Boltzmann’s
analysis.1- Planck then announced
his own program for deriving the
second law of thermodynamics for a
system consisting of radiation and
charged oscillators in an enclosure
with reflecting walls. He would intro-
duce no damping other than radia-
tion damping, but would take the
basic mechanism for irreversibility to
be the alteration of the form of an
electromagnetic wave by the scattering
process— its apparently irreversible con-
version from incident plane to outgo-
ing spherical wave. The ultimate goal
of this program would be the explana-
tion of irreversibility for conservative
systems and, as a valuable by-product,
the determination of the spectral dis-
tribution of black-body radiation.

Planck had high hopes: His goal
was precisely right for a disciple of
Clausius. It would have been a splen
did conclusion to his work in thermo-
dynamics, and it would have put an
end, once and for all, to claims that
the second law was merely a matter
of probability. How was Planck to

MAXWELL

know that he was headed in a very dif-
ferent direction, that he had started
on what he would later call “the long
and multiply twisted path” to the
quantum theory?18

There was, unfortunately, a funda-
mental flaw in Planck’s proposal and
it was promptly pointed out by Boltz-
mann.14 The equations of electrody-
namics could not produce a mono-
tonic approach to equilibrium any
more than the equations of mechanics,
both needed to be supplemented by
appropriate statistical assumptions.
Nothing in the equations of electro-
dynamics wotdd, for example, forbid
the inverse of Planck’s scattering proc-
ess. (It is reasonable to suppose that
Boltzmann was, at the least, not de-
terred from pointing out this error
by Planck’s negative comments on his
own work. Planck’s support of Zer-
melo did not help matters either,
since Boltzmann had found Zermelo's
criticism particularly irksome; Boltz-
mann commented that Zermelo’s pa-
per showed that if, after a quarter of
a century, his work had still not been
understood, at least it had finally been
noticed in Germany!) 10

Planck finally granted that a sta-
tistical assumption was necessary, and
introduced what he called the hypoth-
esis of “natural radiation,” 10 the ap-
propriate analogue of Boltzmann's hy-
pothesis of “molecular chaos,” the hy-
pothesis underlying the H-theorem.17
With the help of this hypothesis
Planck was able to complete his pro-
gram, in a sense, and he reported his

PARTICLES AND QUANTA

297

HUYGENS

work in the last paper of the series in
June 1899. 18 He proved first that the
spectral distribution of the equilib-
rium radiation at temperature T,
p{v,T) (the energy per minute fre-
quency interval at „ in a unit vol-
ume) , was related to the average en-
ergy, E(V,T), of an oscillator of fre-
quency v by the equation,

p{v’T) = (87rv2/c3) E(V,T) (1)

This average energy could be deter-
mined once he fixed the dependence
of the entropy S of the oscillator on
its energy E, but he had no independ-
ent method for determining the func-
tion S ( E ) . He knew, however, that
the spectral distribution had to satisfy
Wien’s displacement law,

p(v.T) = v3 f(v/T) (2)

where / is a function of the ratio
(v/T) only, and that Wien had pro-
posed a particular form of the dis-
tribution that accounted for all avail-
able experimental measurements.10
Wien’s distribution had the form,
p(v,T) = a v3 exp (— /3v/T) (3)

and, with the help of equation 1 and
the thermodynamic definition of the
temperature, this would fix the form
of the entropy function S(E).

Planck proceeded to define S(E) by
— ~ (E//3v) {In E/av) — 1} (4)
the form fixed by equation 3, where
a = (aC3 /&tt) ■ He convinced himself
that this definition was the only possi-
ble one in the sense that if and only
if the entropy had this form could he
prove that the total entropy of the
system increased monotonically to an
equilibrium value. This is what 1
meant when I said that Planck com-

BOLTZMANN

pleted his program “in a sense.” He
had shifted his ground so that he
actually used the second law to fix the
entropy function and thereby the
spectral distribution of the black-body
radiation.

Planck formulated his result in
these words: “I believe that it must
therefore be concluded that the defini-
tion given for the entropy of radia-
tion, and also the Wien distribution
law for radiation that goes with it, are
necessary consequences of applying the
principle of entropy increase to the
electromagnetic theory of radiation,
and that the limits of this law, should
there be any, therefore coincide with
those of the second law of thermody-
namics. For this reason further experi-
mental tests of this law naturally ac-
quires so much the more interest.”

The absolute system of units

This last statement is remarkable
enough in the clear light of our hind-
sight, especially since this paper was
also published, with only minor re-
visions, in the Annalen der Physik
early in 1900, only months before the
introduction of the quantum.20 But
Planck ended his paper with an even
more remarkable section. His expres-
sion for the entropy of an oscillator
(4) contained two constants, a and ft,
which also appear in the Wien distri-
bution law, two universal constants as
Planck called them when he intro-
duced them. He evaluated these con-
stants numerically from the available
experimental data on black-body radi-
ation and found for ft the value

LORENTZ

0.4818 X 10~10 sec °K and for a the
value 6.885 x 10 — 27 erg sec. Planck
observed that these two constants to-
gether with the velocity of light c
and the gravitational constant G could
be used to define new units of mass,
length, time and temperature and that
these units properly deserved the title
of “natural units”.

All systems of units previously em-
ployed owed their origins to the acci-
dents of human life on this earth,
wrote Planck. The usual units of length
and time derived from the size of the
earth and the period of its orbit, those
of mass and temperature from the spe-
cial properties of water, the earth’s
most characteristic feature. Even the
standardization of length using some
spectral line would be quite as arbi-
trary, as anthropomorphic, since the
particular line, say the sodium D line,
would be chosen to suit the conven-
ience of the physicist. The new units
that he was proposing would be truly
“independent of particular bodies or
substances, would necessarily retain
their significance for all times and for
all cultures, including extraterrestrial
and non-human ones,” and therefore
deserved the name of “natural units.”
That they were of awkward sizes
(10—33 cm, 10 — 42 sec. etc) was obvi-
ously of no importance. “These quan-
tities preserve their natural significance
so long as the laws of gravitation and
the propagation of light in vacuum,
and the two laws of thermodynamics
retain their validity.”21

I have referred earlier to Planck’s
conviction that the search for the ab-

298

HISTORY OF PHYSICS

NERNST

CLAUSIUS

solute was the physicist’s proper goal.
The universal constants as well as the
most general physical laws belonged
to that category of the absolute for
him. As he put it in an essay written
in his ninetieth year, “The endeavor to
discover [the absolute constants] and
to trace all physical and chemical
processes back to them is the very
thing that may be called the ultimate
goal of scientific research and study.”23
He had obviously felt the same way
half a century earlier.

It will not have escaped your notice
that the constant he called a in 1899
was soon to be renamed and reinter-
preted. The “further experimental
tests” that Planck had called for were
promptly made, and as the measure-
ments were extended to longer wave-
lengths it became apparent to Planck
that either the second law of thermo-
dynamics did not have universal va-
lidity or there was an error in his
arguments.23 For the Wien distribu-
tion law could not represent the new
data in the infrared. I do not have
space here to recount in detail the ex-
citing events of 1900, but by October
Planck was ready to offer a new distri-
bution law which did account for the
experimental results obtained by his
colleagues Rubens and Kurlbaum, as
well as for all subsequent results on
the black-body radiation spectrum.24
The new law had the now familiar
form,

p(„T) = a,3[exp(/8,/T)-l]-i (5)

Planck’s earlier analysis of the way
that entropy increased with time had
suggested this as the next simplest

possibility after Wien’s law. The prob-
lem was to create a suitable theoretical
foundation for the new distribution
law.

Planck had to take a difficult and
probably painful step. He had to put
aside his opposition to statistical
mechanics and his years of occasional
controversy with Boltzmann and try to
adapt Boltzmann’s methods to his
problem.25 All other resources had
failed him. The crux of the matter
was still the energy-entropy relation
for an oscillator; perhaps Boltzmann’s
equation for the entropy in terms of
the number of complexions could fix
this one missing relationship. Planck
had the great advantage of knowing
what the answer had to be, since his
new distribution law, equation 5, de-
termined the form of the entropy of
an oscillator as a function of its
energy. It too had the kind of logarith-
mic structure that Boltzmann’s equa-
tion would suggest. Using Boltzmann’s
great memoir26 of 1877 as his guide
Planck plunged in, and “after a few
weeks of the most strenuous work of
my life,” as he put it, “the darkness
lifted and an unexpected vista began
to appear.”

“An act of desperation”

In order to calculate the “thermody-
namic probability” of a state in which
a certain energy was shared among
many oscillators of the same frequency,
that is to say, the number of ways in
which this sharing could be accom-
plished, it was essential that Planck
imagine the energy to be composed of

a finite number of identical units,
each of magnitude e. This by itself
would not have been a novel step:
Boltzmann had often done it as a
computational device, particularly in
the 1877 memoir that Planck used as
his guide. But Planck had to refrain
from taking the accepted next step,
namely going to the limit where e
vanishes.27 He had to refrain, that is,
if he were to arrive at the entropy
formula required by the distribution
law that he knew to be the correct
one. He was willing to take this step,
to restrict the energy of one of his
oscillators to multiples of the energy
unit or quantum t, radical though he
must have known it to be.

Thirty years later, in a letter to R.
W. Wood,28 Planck described what he
had done as “an act of desperation,”
undertaken against his naturally
peaceful and unadventurous disposi-
tion. “But,” he went on, “I had al-
ready been struggling with the prob-
lem of the equilibrium of matter and
radiation for six years (since 1894)
without success; I knew that the prob-
lem is of fundamental significance for
physics; I knew the formula that re-
produces the energy distribution in
the normal spectrum; a theoretical
interpretation had to be found at any
cost, no matter how high.” He de-
scribed himself as ready to sacrifice
any of his previous convictions except
the two laws of thermodynamics.
When he found that the hypothesis of
energy quanta would save the day he
considered it "a purely formal assump-
tion, and I did not give it much

THE 1911 SOLVAY CONGRESS brought together many of those who
were interested in quantum theory. Planck is standing second from left.

thought except for this: that I had to
obtain a positive result, under any cir-
cumstances and at whatever cost.”

Planck actually did give his as-
sumption of quanta a good deal of
thought along one particular line. His
theory, which I must omit here, once
again contained two universal con-
stants: the constant k, the proportion-
ality constant that related entropy
to the logarithm of the ‘‘thermo-
dynamic probability,” and the con-
stant h, brought into existence by the
requirements of the displacement law
which made the energy quantum e
proportional to the frequency of the
oscillator, so that c could be ex-
pressed as hv. These constants were
equivalent to those that Planck had
emphasized a year earlier: h was
the former a and k was the ratio
of the former a and R. But now
Planck could discuss their detailed
physical importance as well as their
absolute significance. The constant k,
in particular, had to be equal to the
ratio of the gas constant R to Avo-
gadro’s number N0, the number of
atoms in a gram atomic weight. And
Planck’s determination of k and h
from the measurements on black-body
radiation, with the help of his distri-
bution law in the form
p(r,T) = (8, nri/c3) ( hv ) {exp ( hvjkT )

-l}-1 (6)

gave him an accurate value of Avo-
gadro’s number and with it the mass
of the individual atom.29

This was a major achievement.
Planck’s value for Avogadro’s number
was far more accurate than any of the
existing indirect estimates based on
the kinetic theory of gases, and he used
it not only to get the mass of the atom
but also, together with the Faraday

constant, to determine the charge on
the recently discovered electron, the
natural unit of electric charge. His
value of e was 4.69 X 10-10 e.s.u.— at
a time when the early attempts at
direct measurement gave results from
1.3 to 6.5 in the same units. Unfor-
tunately, Planck’s contemporaries did
not properly appreciate these results;
the handbooks went on printing crude
determinations of Avogadro’s number,
ignoring Planck's value.30 The first ex-
perimentalist to quote Planck’s value
of e seems to have been Rutherford, in
1908, probably because he and Geiger
had obtained essentially the same
value, 4.65 X lO-10 e.s.u. from the
charge on the alpha particle and were
glad to have a confirmation of a re-
sult 50% higher than J. J. Thomson’s
current best determination.31

Planck himself laid heavy emphasis
on these concrete results of his theory,
both in his papers and in his Lectures
on the Theory of Heat Radiation 32
published in 1906. I am convinced
that, with Planck’s particular sensi-
tivity to the importance of the natural
constants, it was these results that as-
sured him that quanta were more than
an ad hoc hypothesis, useful only for
arriving at the radiation law. Of
course h, the second constant in his
equation, the essentially new constant
in the theory, was yet unexplored. He
remarked in his Lectures at several
points that h must have some direct
electrodynamic meaning, that this
meaning must be found before the
theory of radiation could be consider-
ed fully satisfactory, but that a lot
more research would be needed be-
fore this meaning was revealed.

The kind of electrodynamic mean-
ing that Planck had in mind for h

was suggested in a letter he wrote to
Paul Ehrenfest33 in July 1905. Ehren-
fest was engaged in an analysis of
Planck’s assumptions and had written
to Planck asking several questions
about them. In his answer Planck
pointed out that the existence of a
discrete unit of electric charge im-
posed certain limitations on the elec-
tromagnetic field. He went on to
write: “Now it seems to me not com-
pletely impossible that there is a
bridge from this assumption (of the
existence of an elementary quantum
of electric charge e) to the existence
of an elementary quantum of energy
h, especially since h has the same di-
mensions and also the same order of
magnitude as (e2/c) . But I am not in
a position to express any definite con-
jecture about this.” Planck never pub-
lished this remark, so far as I can tell.
Almost the same thought, however,
was expressed by Einstein in 1909 in
the course of a dimensional analysis
of the displacement law.34 He too
pointed out the dimensional equiva-
lence of h and ( e2/c ). But I am not in
noted, correctly, that their magnitudes
differed by a factor of about a thou-
sand. “The most important thing in
this derivation,” Einstein went on,
“is that it reduces the constant for
light quanta h to the elementary unit
of electricity e. Now one must remem-
ber that the elementary charge e is
a stranger in the Maxwell-Lorentz
electrodynamics. ... It seems to me
to follow from the relationship,
h=e2/c, that the same modification
of the theory which contains the ele-
mentary charge as one of its conse-
quences will also contain the quantum
structure of radiation.”

Retreat from energy quantization

I have been trying to give the back-
ground for my earlier statement that
Planck was fully committed to the
quantum, but not necessarily to a
quantum theory in Einstein’s sense.
Planck’s work in the years after 1910,
when he resumed publication in this
field shows him holding fast to the
quantum of action but retreating
steadily from his earlier strict quanti-
zation of the oscillator. In a paper35
read to the German Physical Society
in February 1911 he explained that
he was revising his original theory

300

HISTORY OF PHYSICS

because of the valid criticism to which
it had been subjected, particularly
by H. A. Lorentz.36 The objection
was basically that the intensity of the
radiation at high frequencies was
very low, whereas at these frequencies
the energy quantum was very large.
As a consequence the time it would
take an oscillator to absorb one
quantum would have to be unreason-
ably long, and the oscillator might
not even be able to absorb one full
quantum if the radiation should be
cut off. This criticism naturally pre-
supposed that radiation was properly
described by electromagnetic waves,
and it is interesting to note that
Lorentz had used this argument to
show how difficult it was to explain
phenomena like the photoelectric ef-
fect without having recourse to Ein-
stein’s light quanta instead of the
wave description. Planck, however,
did not take it that way.

He proposed instead to give up his
hypothesis that the energy of an oscil-
lator had to be an integral multiple
of hv and could therefore absorb or
emit energy only in discrete units. In
his new theory the oscillator would
absorb energy continuously, just as it
did classically, so that Lorentz’s criti-
cism could be set aside. The emission
process, however, was still quantized.
This procedure would eliminate an-
other difficulty, an internal contradic-
tion in the original theory pointed out
by Einstein.37 In that theory Planck
had used the classically derived rela-
tionship between the radiation density
and the oscillator’s energy, but that
classical derivation was, of course, in-
compatible with the assumption of
quantum states for the oscillator.

Planck gave several versions of his
new theory of quantized emission in
1911 and 1912, finally settling on one
in which the oscillator, absorbing
energy continuously, could emit only
when its energy was a multiple of
hv-S8 If it emitted at all it had to
emit all the energy it possessed, how-
ever many quanta that might be.
Whether or not it emitted as its
energy reached nhv, for any n, was
governed by a probability rj- This
probability was fixed by the assump-
tion that the ratio of the probability
of no emission to the probability of
emission, (1— 77/77), should be propor-

tional to the intensity of the inci-
dent radiation. The proportionality
constant, in turn, was determined by
the requirement of classical behavior
in the limit of high intensity radia-
tion. (This is surely one of the first
uses of the correspondence principle.
There is reason to believe that this
paper of Planck’s had considerable
influence on Bohr’s first papers on
atomic structure.39)

This second quantum theory of
Planck’s led to the same law for
black-body radiation as had the first
(this must have been an unexpressed
boundary condition on the work).
But it made an interesting change
in the expression for the average
energy of an oscillator,

E = hv (exp(hv/kT) — \}~i +

hv/ 2 (7)

The additional term meant that the
energy of an oscillator would not
vanish at the absolute zero of tem-
perature but would be just (h v/2) ;
hence its usual name of zero-point
energy. Planck saw a variety of phe-
nomena that might be interpreted as
favoring his concept of quantum emis-
sion, and also some that supported
the reality of the zero-point energy.
He suggested, for example, that this
might be the source of the energy
of particles emitted by radioactive
atoms, and that the sharply defined
energy of these particles was an ex-
ample of quantum emission.

The novel idea of zero-point energy
attracted a good deal of attention,
first of all from Einstein, as one might
have expected. Early in 1913 he and
Otto Stern discussed its possible rele-
vance for understanding Eucken’s
new measurements of the heat capac-
ity of hydrogen gas at low tempera-
tures.40 A number of physicists then
tried to apply the zero-point energy
to phenomena as diverse as devia-
tions from Curie’s law in paramag-
netism41 and the equation of state
of gases.42 The most significant ap-
plication was made by Debye in his
theory of the effect of thermal vibra-
tions on x-ray scattering from crys-
tals.43 Debye showed that the presence
or absence of the zero-point energy
could be brought to experimental test
by a study of the intensities of x-ray
diffraction spots. This was eventually
done, and the existence of zero-point

energy was confirmed, but by that
time it had lost its connection with
Planck’s largely forgotten second
quantum theory.44

For Planck the zero-point energy
was an interesting by-product of his
work, but the important thing was
that he had arrived at the radiation
law without having to restrict the
energy of the oscillator to quantized
energies. Actually he was ready to
give up even the quantized emission
of radiation, and did so in a paper
he wrote in 1911, where the crucial
h governed only the interaction be-
tween oscillators and free particles,
and the absorption and emission of
radiation followed the classical laws.45
Planck was always arguing to the
radiation law and tried to restrict the
use of the quantum to the minimum
sufficient for deriving that law.

Nernst’s lari’, entropy and quanta

Planck’s book on radiation included
one important new step in the search
for an understanding of h. He con-
structed an argument showing that
h could be interpreted directly as a
quantum of action in the sense that
h measured the areas of the regions
of equal statistical weight in the phase
space of the oscillator.40 The concept
of a cell in phase space had already
played an important part in Boltz-
mann's statistical mechanics, but as
Planck emphasized in his parallel dis-
cussion of the ideal gas, its magnitude
was apparently of no significance
there since it appeared only in the
additive constant in the entropy.

At this stage he did not yet see
that there was anything general about
the use of h to fix the size of a
cell in phase space.

The lectures on heat radiation on
which Planck’s book were based were
delivered during the winter semester
of 1905-1906, and while they were
going on, Planck’s colleague at Ber-
lin, Nernst, reported a significant ad-
vance in thermodynamics.47 This
was Nernst’s famous heat theorem
which, although he did not formulate
it that way, amounted to the state-
ment that the entropy differences
between all states of a system dis-
appear at absolute zero. It is clear
that a new result in thermodynamics
of such general import would have

PARTICLES AND QUANTA

301

been of interest to Planck, but it
is not so dear, in view of Planck’s
background as I have described it,
that he should have been the one to
probe its statistical significance as
well.

He discussed his views in a lecture
entitled “On Recent Thermodynamic
Theories: Nernst’s Heat Theorem
and the Hypothesis of Quanta,” deliv-
ered before the German Chemical
Society in December 191 1.48 Planck
described the importance of Nernst’s
theorem, which was really a new and
independent postulate, by pointing
out the incompleteness of the classical
thermodynamics based on the first
and second laws. Classical thermo-
dynamics could not lead to a full
specification of the conditions for
equilibrium (phase equilibrium or
chemical equilibrium) precisely be-
cause it provided no way of fixing
the undetermined constant in the
entropy equation. Just this gap was
filled by Nernst’s law, and Planck
stated it in what he considered its
simplest and most far-reaching form:
the entropy of a chemically pure
substance in a condensed phase van-
ishes at absolute zero. Nernst’s law,
in other words, allowed one to fix
the absolute value of the entropy
and therefore represented a major
addition to thermodynamics.

Planck then went on to ask for
‘‘the real, the more profound physico-
chemical meaning” of the law, that
is, its meaning on the atomic scale,
not only because this promises

OSTWALD

greater intuitive insight, but also
because only it can help one to dis-
cover regularities and relationships
. . . which pure thermodynamics can-
not touch.” And this atomistic inter-
pretation of a law involving the en-
tropy would have to be found, he
said, by using Boltzmann’s fundamen-
tal relationship between entropy and
probability. Planck had come a long
way in his thinking in the decade or
so since he had reconciled himself to
trying Boltzmann’s methods!

If one wanted to calculate the
entropy of a system with the help of
Boltzmann’s relationship, the whole
procedure was fully determined ex-
cept for one point: there was no a
priori criterion for choosing the size
of the elementary cells in phase space.
This lack of definiteness was the
exact counterpart of, and could be
considered the reason for, the in-
determinateness of the entropy con-
stant (as mentioned earlier) . Con-
versely, then, if Nernst’s law fixed
the entropy constant, this must imply
that its “deeper meaning” must be
that the sizes of the cells in phase
space are not arbitrary but must have
definite tallies. This statement would
have been hard to accept, Planck
went on, if not for the totally un-
expected support it received from
the theory of black-body radiation,
that is from his own interpretation
of h as precisely the size of the
phase cell for oscillators of any fre-
quency. Further analysis of the “mean-
ingful and attractive problem” of

EINSTEIN

determining these quite definite ele-
mentary cells for calculating the ther-
modynamic probability was called for,
since Planck now saw this as the
essential content of the hypothesis
of quanta.

He put it this way some months
later in the preface to the second
edition of his book on heat radia-
tion.41’ “For the hypothesis of quanta
as well as the heat theorem of Nernst
may be reduced to the simple propo-
sition that the thermodynamic proba-
bility of a physical state in a definite
integral number, or what amounts to
the same thing, that the entropy of
a state has a quite definite, positive,
value, which, as a minimum, becomes
zero, while in contrast therewith the
entropy, may, according to the clas-
sical thermodynamics, decrease with-
out limit to minus infinity. For the
present, 1 would consider this prop-
osition as the very quintessence of
the hypothesis of quanta.” Planck
must have been thoroughly gratified
to have found this way of relating
his two favorite concepts— entropy and
the quantum of action. He devoted
much thought to the general prob-
lem of determining the size and shape
of the elementary cells in phase space
over the next decade, no but I cannot
discuss that work here.

“A far more significant part”

In the Scientific Autobiography that
he wrote near the end of his long
life Planck frankly discussed the at-
titude prevalent among many physi-

WIEN

302

HISTORY OF PHYSICS

cists about his work after 1901. 51
“My futile attempts to fit the ele-
mentary quantum of action somehow
into the classical theory continued for
a number of years, and they cost me
a great deal of effort. Many of my
colleagues saw in this something bor-
dering on a tragedy. But I feel dif-
ferently about it. For the thorough
enlightenment I thus received was
all the more valuable. I now knew
for a fact that the elementary quan-
tum of action played a far more
significant part in physics than I
had originally been inclined to sus-
pect.”

It was in this same spirit that he
had prophetically closed his lecture
to the German Chemical Society in
1911. “To be sure, most of the work
remains to be done; . . . but the
beginning is made: the hypothesis of
quanta will never vanish from the
world. . . . And I do not believe
I am going too far if I express the
opinion that with this hypothesis the
foundation is laid for the construction
of a theory which is someday des-
tined to permeate the swift and deli-
cate events of the molecular world
with a new light.” □

All quotations from Planck's unpub-
lished letters are made with the kind
permission of Frau Dr. Nelly Planck, to
whom I should like to express my thanks.

For an analysis coming to rather different
conclusions see Thomas S. Kuhn, Black-Body
Theory and the Quantum Discontinuity,
1894—1912 (New York, 1978). See also Allan
A. Needell, Irreversibility and the Failure of
Classical Dynamics: Max Planck’s Work on
the Quantum Theory 1900-1915 (Yale Univ.
PhD. Diss., 1980).

References

Planck’s scientific papers are collected in
three volumes: Physikalische Abhand-
lungen und Vortrage (Friedrich Vieweg &
Sohn, Braunschweig, 1958). Referred to
below as Papers.

1. M. Planck, Ann. Phys. (4) 31, 758
(1910); Papers II, 237.

2. M. Planck to W. Nernst II June 1910.
This letter is quoted in full in an
unpublished manuscript by Jean Pel-
seneer entitled “Historique des Insti-
tuts Internationaux de Physicpie et de
Chimie Solvay.” The manuscript is
part of the archive “Sources for the
History of Quantum Physics,” at the
Library of the American Philosophical
Society in Philadelphia.

3. M. Planck, Scientific Autobiography
and Other Papers, translated by F.
Gaynor (Philosophical Library, New
York, 1949) p. 35.

4. M. Planck, Ann. Phys. (3) 57, 72
(1896); Papers I, 459.

5. M. Planck, Treatise on Thermody-
namics, (1897) translated by A. Ogg.
(Longmans, Green, and Co., London,
1903), Preface.

6. M. Planck, Z. phys. Chem. 8, 647
(1891); Papers 1, 372.

7. M. Planck, Z. f. phys. und chem. Un-
terricht 6, 217 (1893); Papers I, 437.

8. M. Planck, Ann. Phys. (3) 57, 1 (1896);
Papers I, 445.

9. W. Wien, Ann. Phys. (3) 52, 132
(1894).

10. M. Planck, Ann. Phys. (3) 60, 577
(1897); Papers I, 466.

11. M. Planck, S.-B. Preuss. Akad. Wiss.
(1897), p. 57; Papers I, 493.

12. E. Zermelo, Ann. Phys. (3) 57, 485
(1896), 59, 793 (1896); Also see R.
Dugas, La theorie physique au sens
de Boltzmann (Editions Griffon, Neu-
chatel, Suisse, 1959) pp. 206-219.

13. M. Planck, Nobel Prize Address in
A Survey of Physical Theory re-
printed (Dover, New York, 1960), p.
102; Papers III, 121.

14. L. Boltzmann, S.-B. Preuss. Akad.
Wiss. (1897) pp. 660, 1016, (1898)

p. 182.

15. L. Boltzmann, Ann. Phys. (3) 57, 773
(1896). Also his Populdre Schriften
(Barth, Leipzig; 1905) p. 406.

16. M. Planck, S.-B. Preuss. Akad. Wiss.
(1898), p. 449; Papers I, 532.

17. See, for example, P. and T. Ehrenfest,
The Conceptual Foundations of the
Statistical Approach in Mechanics,
translated by M. J. Moravcsik (Cornell
University Press, Ithaca, N.Y., 1959)
p. 41.

18. M. Planck, S.-B. Preuss. Akad. Wiss.
(1899), p.440.; Papers I, 560.

19. W. Wien, Ann. Phys. (3) 58, 662
(1896).

20. M. Planck, Ann. Phys. (4) 1, 69
(1900); Papers I, 614.

21. See references 18 and 20. I would like
once again to thank Dr. Joseph Agassi
for calling my attention to Planck’s
pre-quantum determination of h.

22. Op. cit. reference 3, p. 78.

23. M. Planck, Ann. Phys. (4) 1, 719
(1900); Papers I, 668.

24. M. Planck, Verh. d. Deutsch. Phys.
Ges. 2, 202 (1900); Papers I, 687.

25. See M. J. Klein, Archive for History
of Exact Sciences I, 459 (1962), and
The Natural Philosopher (Blaisdell
Publishing Company, New York) 1,
81 (1963). Also see K. A. G. Mendels-
sohn in A Physics Anthology, edited
by N. Clarke (Chapman and Hall,
London, 1960), p. 62 and L. Rosen-
feld, Osiris 2, 149 (1936).

26. L. Boltzmann, Wien. Ber. 76, 373
(1877).

27. M. Planck, Verh. d. Deutsch. Phys.
Ges. 2, 237 (1900); Papers I, 698; Ann.
Phys. (4) 4, 553 (1901); Papers I, 717;

Also the papers of reference 25.

28. M. Planck to R. W. Wood, 7 October
1931. This letter is part of the collec-
tion in the Archives of the Center for
the History and Philosophy of Physics
of the American Institute of Physics
in New York City.

29. See the first article in reference 27
and also M. Planck, Ann. Phys. (4) 4,
564 (1901); Papers I, 728.

30. G. Hertz in Max Planck zum Geden-
ken (Akademie-Verlag, Berlin, 1959)
pp. 33-35.

31. E. Rutherford and H. Geiger, Proc.
Roy. Soc. A 81, 162 (1908).

32. M. Planck, Vorlesugen tiber die
Theorie der Wdrmestrahlung (Barth,
Leipzig, 1906) p. 162.

33. M. Planck to P. Ehrenfest, 6 July
1905. This letter is part of the Ehren-
fest collection at the National Muse-
um for the History of Science in
Leyden.

34. A. Einstein, Phys. Z. 10, 192 (1909).

35. M. Planck, Verh. d. Deutsch. Phys.
Ges. 13, 138 (1911); Papers II, 249.

36. H. A. Lorentz, Phys. Z. 11, 1248
(1910). This is actually a report by
Max Born of Lorentz’s Wolfskehl lec-
tures, "Alte und neue Fragen der
Physik.”

37. A. Einstein, Ann. Phys. (4) 20, 199
(1906).

38. M. Planck, Ann. Phys. (4) 37, 642
(1912); Papers II, 287."

39. See T. Hirosige and S. Nisio, "Forma-
tion of Bohr’s Theory of Atomic
Constitution,” Japanese Studies in
the History of Science No. 3, p. 6
(1964).

40. A. Einstein and O. Stern, Ann. Phys.
(4) 40, 551 (1913).

41. E. Oosterhuis, Phys. Z. 14, 862 (1913).

42. W. H. Keensom, Phys. Z. 14, 665
(1913).

43. P. Debye, Ann. Phys. (4) 43, 49
(1914).

44. R. W. James, I. Waller, and D. R.
Hartree, Proc. Roy. Soc. A118, 334
(1928). See also Fifty Years of X-Ray
Diffraction, P. P. Ewald, ed. (Oos-
thoek, Utrecht 1962), pp. 126, 230.

45. M. Planck, S.-B. Preuss. Akad. Wiss.
(1914) p. 918; Papers II, 330.

46. Op. cit. reference 32, pp. 154-156.

47. W. Nernst, Gott. Nachr. (1906), p. 1.
See also F. Simon’s Guthrie Lecture
in Yearbook of the Physical Society
of London 1956, p. 1.

48. M. Planck, Phys. Z. 13, 165 (1912);
Papers III, 54.

49. M. Planck, The Theory of Pleat Radi-
ation, translated by M. Masius 2nd
Ed. (1913), reprinted (Dover, New
York, 1959), p. vii.

50. See his Wolfskehl Lecture of 1913 in
Vortrage uber die kinetische Theorie
der Materie und der Elektrizitdt
(B. G. Teubner, Leipzig, 1914) p. 3;
Papers II, 316. Also see L. Rosenfeld in
Max-Planck-Festschrift 1978 (Deutch-
er Verlag der Wissenchaften, Ber-
lin 1959), p.203.

51. Op. cit. reference 3, p. 44.

PARTICLES AND QUANTA

303

J. J. Thomson
and the Bohr atom

Far from being merely “scientific curiosities,” J. J. Thomson’s
seemingly naive models actually contained some of the fundamental ideas
of Niels Bohr’s revolutionary quantum theory of the atom.

John L. Heilbron

PHYSICS TODAY / APRIL 1977

In 1911 Niels Bohr went to Cambridge,
hoping to talk physics with J. J. Thomson;
the discoverer of the electron was friendly
but uninterested. Two years later Bohr
published his epochal three-part paper on
the constitution of atoms and molecules,
which challenged the program and goal of
the Cambridge school. Bohr’s new views
soon won out; Thomson’s quaint atomic
models were declared worthless — old
lumber fit only, as Ernest Rutherford put
it, “for a museum of scientific curiosities.”
For his part Thomson rejected the ad-
vances made by Bohr as meretricious su-
perficialities obtained without, or at the
price of, an understanding of the mecha-
nism of atoms.

As in many other instances in the his-
tory of science, Bohr’s revolutionary
theory became such a success that its or-
igins in the views it superseded were all
but forgotten. In particular, Thomson’s
opposition and the quick replacement of
his research program by Bohr’s obscured
the connection between the theory of the
quantized atom and the deceptively sim-
ple and apparently naive models of the
Cambridge school. So has the odd cir-
cumstance that the three installments of
Bohr’s first paper on atomic structure
inverted the order of his discoveries. The
first installment, the only one now re-
membered, gives the theory of the Balmer
spectrum, which Bohr worked out in a few
weeks in February 1913; the other two
record Bohr’s attempts, beginning in June
1912, to bring Rutherford’s nuclear
model — itself a product of Thomson’s
research program — to bear on the chief
problems of atomic theory as Thomson
had identified them.

John L. Heilbron is professor of history and di-
rector of the Office for History of Science and
Technology, University of California, Berke-
ley.

To Thomson the key problem in atomic
theory was the explanation of the varia-
tion in the periodic properties of the
chemical elements represented in Men-
deleev’s table. Already in 1897, when
announcing the discovery of the electron,
he intimated that the new particles might
well provide this periodicity when they
are bound into an atom. Not then
knowing how this might be accomplished,
he resorted to the sort of analogy charac-
teristic of the Cambridge school of
mathematical physics during Thomson’s
time.

Magnets and a plum pudding

As an analogue to the arrangement of
electrons in an atom, Thomson offered
Alfred Mayer’s floating magnets, which
distribute themselves into concentric
circles under the influence of a large sta-
tionary magnet, as shown in figure 1. In
1903, having secured the electron, mea-
sured its charge and mass, and laid the
foundation of the electron theory of
metals, Thomson took up the question
how his favorite corpuscle could play the
part of Mayer’s magnets.

The first problem was to choose a rep-
resentation for the positive portion of the
atom. The arrangement that is perhaps
the most obvious, the nuclear model, had
already been proposed and discarded on
the ground of mechanical instability: In
any Saturnian atom — one with several
electrons arranged in a plane ring or
rings — there exists at least one unstable
mode of oscillation about the equilibrium
orbits. The amplitudes of these unstable
modes grow until the system flies apart.
However, a stable variant can be obtained
by allowing the positive charge to fill the
entire volume of the atom; the electrons
then circulate within the positive charge,
subject to a restoring force varying di-
rectly as the distance rather than as its

inverse square. This so-called “plum-
pudding model” is the one Thomson
adopted.

Note that the instability that led to the
initial rejection of the nuclear model was
a mechanical one: It did not derive from
that drain of energy by radiation that
plays so important a role in the standard
historical accounts. Indeed, as Thomson
showed, the total radiation from a ring of
p symmetrically placed electrons de-
scribing the same circular orbit decreases
very rapidly as p increases; for moderate
values of p the ring — and hence the
atom — has almost eternal life.

Even the eventual mortality of atoms
was no inconvenience to Thomson: He
merely associated radioactivity with an-
cient atoms, the internal motions of which
had decayed to the point of instability and
explosion. At this time (1904) he thought
that the atom contained a great many
electrons, perhaps — as the richness of
spectral lines and the ratio of the masses
of the electron and the hydrogen ion
suggest — as many as a thousand times the
atomic weight. He did not lack particles
to populate his rings and plug the radia-
tion drain.

The urge of individual electrons in an
atom to radiate can therefore be curbed
by the social pressure of their neighbors.
But this pressure can not be driven too
far: Electrons are not friendly; they repel
one another. When enough of them are
assembled in a ring to extinguish their
radiation, there may be too many for
mechanical stability; a little disturbance
to any one of them might cause the ring to
fly apart. Thomson conceived the idea
that the condition of mechanical stability
might be the clue to the periodicity in the
electronic arrangements of the atoms.
The electrons’ need for elbow room might
fix their population distribution. In 1904
he put this idea to the test.

304

HISTORY OF PHYSICS

Mayer’s magnets — magnetized needles floated on corks, under a large
stationary magnet — provided J. J. Thomson with an analogy to the ar-
rangements of electrons in atoms. These diagrams, made by pressing
paper against the inked tops of the magnets, displayed stable configu-
rations with a periodicity suggestive of Mendeleev's table. From A. M.
Mayer, Am. J. Science 116, 248 (1878). Figure 1

Rutherford’s first calculations on the passage of alpha particles through
atoms. In his “theory of structure of atoms,” Rutherford used a nuclear
atom that was a variant of Thomson’s model, of electrons in a sphere of
positive charge: It had a positive central nucleus of charge ne surrounded
by a diffuse sphere of negative electricity. From the Rutherford Papers.
Cambridge University Library. Figure 2

The heart of Thomson’s analysis was
the calculation of the frequencies of the
perturbed oscillations of the electrons in
a single-ring atom as a function of their
number p. He hoped to learn from the
frequencies how large p might be before
mechanical instability set in: The num-
ber turned out to be six. To accommo-
date more electrons in a single ring, the
rate at which the restoring force varied
with distance had to be greater than that
afforded by the diffuse charge alone.

Rings of electrons

Nothing could be simpler than in-
creasing this rate: One needed merely to
put one or more electrons ( q in all, say) at
the atom’s center. Thomson calculated
the values of q that would result in a sta-
ble outer ring of p electrons. It turned
out that the inner electrons themselves
must be distributed in rings, and that for
each value of the total electron popula-
tion, n = p + q, the distribution is
unique.

This distribution represents an elec-
tronic parallel to Mayer’s magnets, but
one that is far more suggestive of the
physics of atoms. Thomson shows that
if p = 20, q must lie between 39 and 47,
inclusive; his results are presented in
Table 1. If q is close to the minimum, the

atom could increase its stability by losing
one of its 20 outer electrons; such an atom
would act electropositively. If q is near
a maximum, the atom would tend to gain
an electron, and therefore act electrone-
gatively. The models characterized by p
= 20 consequently offered a striking
analogy to the elements of the second and
of the third periods of Mendeleev’s
table.

It was this elucidation of the periodic
table, expanded and translated into
German, that brought continental phys-
icists an inkling that something might
come from the Cambridge theory of
atomic structure. In 1909 Max Born
thought Thomson’s model sufficiently
promising to take it as the subject of his
inaugural lecture as Privatdozent , and in
1911 Arnold Sommerfeld’s physics collo-
quium studied it with the help of floating
magnets.

“If it resembled a little, it was so”

Three points about Thomson’s analogy
deserve attention:

► He has introduced the fundamental
idea that atoms of successive elements in
the periodic table differ from one another
by the addition of a single electron.

► He has, from a modern point of view,
interchanged the roles of core and valence

electrons. The atoms of each period are
characterized by the same number of ex-
ternal electrons, and differ only in the
populations of their inner rings. Chem-
ical and optical properties consequently
derive primarily from the deeper-lying
electrons; the members of a chemical
family have only internal structures in
common. Likewise all the electrons in
the atom, and not just the deepest, are
implicated in radioactivity, and it is
therefore difficult to find room in
Thomson’s scheme for structures with
identical chemical and different ra-
dioactive properties. The existence of
isotopes, as Bohr later emphasized, could
not be explained plausibly on the basis of
the diffuse-sphere atom.

► Lastly, despite the mathematical labor
that secured it, Thomson’s analogy was
essentially qualitative. Here we reach a
perplexing and perennial characteristic of
Thomson’s physics. At the very begin-
ning of his career, in 1882, he had won the
prestigious Adams Prize at Cambridge for
a lengthy essay on Kelvin’s vortex atoms.
To describe encounters between such
atoms, which resembled smoke rings in
air, required severe and rigorous calcula-
tions, the application of which to physical
or chemical phenomena proved all but
impossible. Already then Thomson had

PARTICLES AND QUANTA

305

Margrethe Norlund and Niels Bohr announce their engagement in 1911. That year Bohr defended
his thesis at the University of Copenhagen and left for the Cavendish Laboratory. Figure 3

to content himself with the sort of quali-
tative and suggestive connections he was
later to make with his electronic atom.
He never identified particular chemical
atoms with definite models, whether
vortical or electronic. “Things needed
not to be very exact for Thomson,” Bohr
used to say, “and if it resembled a little, it
was so.”

The most important undetermined
parameter in Thomson’s model was the
total electron number n. On its magni-
tude depended not only the security of the
atom against radiation collapse, but also
inferences about the nature of positive
charge and the process of spectral emis-
sion. Thomson worked on the problem
for five or six years, bringing to bear his
powerful mathematics and the experi-
mental resources of the Cavendish Lab-
oratory. He was the first to explore the
atom by shooting charged particles
through it, and the first to work out for-
mulas, including probability consider-
ations where appropriate, for the scat-

tering of x rays and beta rays.

The chief result of comparing the ex-
periments to the formulas was that n was
about equal to the atomic weight A . The
outcome of Rutherford’s variant of
Thomson’s scattering theory — alpha
scattering elucidated by the nuclear
atom — was an n of about A/2. That the
nuclear atom was an outgrowth of
Thomson’s research program appears
plainly from the first page of Rutherford’s
first calculations on the “theory of the
structure of atoms,” reproduced in figure
2. Note the depiction of the scatterer as
a tiny positive nucleus of charge ne, sur-
rounded by a diffuse sphere of negative
electricity of fixed radius.

The thousandfold reduction of the
atomic population brought Thomson and
his co-workers very close to the doctrine
of atomic number. It also made acute the
problem of the radiation collapse of light
atoms. It was quite characteristic of
Thomson to acknowledge this unpleas-
antness and move on; he considered

spectra too complicated to reveal any-
thing useful about atomic structure — and
in this opinion too he was followed by
Bohr.

Bohr’s approach

Bohr came to the problem of atomic
structure almost by chance. His subject
had been the electron theory of metals, on
which he had written a thesis defended at
the University of Copenhagen in the
spring of 1911. He then went to the Ca-
vendish Laboratory, intending to rework
his thesis for English publication. And
why the Cavendish?

“I considered first of all Cambridge as
the center of physics,” Bohr later said of
his decision to study there, “and Thomson
as a most wonderful man . . ., a genius who
showed the way for everybody.” Thom-
son received him politely and promised to
read the rough translation of his thesis
that Bohr had brought him.

“I have just talked to J. J. Thomson,”
Bohr wrote his brother after his first in-
terview, “and I explained to him as well as
I could my views on radiation, magnetism,
etc. Y ou should know what it was for me
to talk to such a man. He was so very
kind to me; we talked about so many
things; and I think he thought there was
something in what I said. He has prom-
ised to read my thesis, and he invited me
to have dinner with him next Sunday at
Trinity College, when he will talk to me
about it . . .”

The exchange of views Bohr desired did
not take place. Thomson, who had long
before given up active cultivation of the
electron theory, probably never read
Bohr’s thesis; in any case he did not enjoy
having his ancient errors rehearsed by a
tenacious foreigner whose English he
could scarcely understand. But even had
language and divergent interests not been
barriers, one doubts that the intellectual
communion that Bohr sought could have
developed.

For one thing, the imprecise and con-
tradictory analogies Thomson fancied
were inadequate for Bohr, who sought
coherent, consistent models from which
quantitative predictions about experi-
mental results might be drawn. For an-
other, Thomson, though friendly and re-
ceptive to questions, worked alone; he
seldom solicited his students’ views on
scientific questions, nor did he develop his
own through extended conversations with
others. Bohr’s life-long practice, on the
other hand, was to refine his ideas in
lengthy discussions, which often became
monologues, with informed individuals.
Whether his colloquist was a full collab-
orator, a sounding board or an amanu-
ensis, he required some human contact at
almost every stage of his work.

It is perhaps not too fanciful to see a
reflection of their styles in their photo-
graphs. Figure 3 shows Bohr about 1911,
aged 26, boyish, callow, soft-featured and
gentle. With him is one of his aman-

306

HISTORY OF PHYSICS

J. J. Thomson in 1909. In 1896 Rutherford had written of his ' most radiating smile . . . when
scoring off anyone.” (Photo in G. P. Thomson, J. J. Thomson, Doubleday, 1965) Figure 4

uenses, his future wife Margrethe, who
wrote out his first papers on atomic
structure. Figure 4 portrays Thomson at
about the same time, aged 53. He had not
changed much since his discovery of the
electron.

“You ask whether J.J. is an old man,”
Rutherford had written his fiancee in
1896. “He is just 40 and looks quite
young, small, rather straggling moustache,
short, wears his hair (black) rather long,
but has a very clever-looking face, and a
very fine forehead and a most radiating
smile, or grin as some call it, when he is
scoring off anyone.”

A little piece of reality

Thomson’s indifference by no means
deflected Bohr from the pursuit of the
electron theory. It was the chief subject
of his research throughout the eight
months he spent at Cambridge, and it
remained so during the first three months
of his stay at Manchester, where he moved
in March 1912, to learn something of the
experimental side of radioactivity. It is
important to recognize that Bohr did not
go to Manchester, Rutherford’s citadel, to
help develop the consequences of the
nuclear atom. He went to take a six-week
course on experimental technique, a
standard service of the laboratory for
beginners in radioactivity, after which
they usually began a small research task
proposed by Rutherford. Figure 5 shows
a page of Bohr’s carefully kept laboratory
notebook.

It was not that Bohr wished to become
an experimentalist: His object was to
capitalize on his time in England, and to
make contact with Rutherford, evidently
the coming power in English physics.
After finishing the laboratory work for the
day he would return to the electron theory
of metals.

Bohr came to atomic physics in a casual
way. The research topic Rutherford had
assigned him was interrupted for want of
radium emanation (radon). While wait-
ing for more to grow he studied a paper on
the absorption of alpha particles that had
just been published by C. G. Darwin, the
only mathematical physicist besides
himself in Rutherford’s group. Bohr
found that Darwin’s treatment rested on
an unsatisfactory assumption about the
interaction between alpha particles and
atomic electrons: Darwin had ignored
the binding forces. Bohr, following a
technique used by Thomson, proposed to
take the forces into account by treating
the interaction as a resonance phenome-
non depending on the ratio of l/i/, the
natural period of the electrons’ vibrations
about equilibrium, to the time required by
an alpha particle to pass the atom.

Bohr expected to make an easy calcu-
lation, which would quickly furnish a
short note for the Philosophical Maga-
zine; that was in early June, 1912. By the
middle of the month he had abandoned
the laboratory, shelved the electron

theory and given himself up entirely to
the design of atomic models. A letter
from Bohr to his brother Harald, dated 12
June 1912, gives a clue to what hap-
pened:

“It could be that I’ve perhaps found
out a little bit about the structure of
atoms. You must not tell anyone
anything about it; otherwise I certain-
ly could not write you this soon. If
I’m right, it would not be an indica-
tion of the nature of a possibility (like
J. J. Thomson’s theory) but perhaps a
little piece of reality. It has all grown
out of a little piece of information I
obtained from the absorption of alpha
particles ... You can imagine how
anxious I am to finish quickly and I’ve
stopped going to the laboratory for a
couple of days to do so (that’s also a
secret).”

And what was the “little piece of infor-
mation”? It may well have been the
discovery that the nuclear atom is me-
chanically unstable.

Thomson and the Cambridge school
had rejected the nuclear model on account

of its mechanical instability; Bohr wel-
comed it precisely because it needed a
nonmechanical force to exist. Already in
his Copenhagen dissertation he had
pointed to certain phenomena — heat ra-
diation and paramagnetism in particu-
lar— that eluded the electron theory and
appeared to require the ascription of a
nonmechanical rigidity to the paths of
atomic electrons. He was drawn to the
nuclear model as a possible representation
or reification of the sorts of difficulties he
had encountered in his earlier studies.

Bohr’s fiat

To make further progress possible he
exempted, by fiat, electrons that describe
closed orbits satisfying the condition

T = Kv' (1)

(where T is the electron’s kinetic energy,
v' its orbital frequency and K a constant)
from the ordinary necessities of their ex-
istence: They did not radiate energy and
they did not respond to small perturba-
tions. Electrons so characterized, elec-
trons in their ground or permanent state,

Table 1. A Thomson atom with twenty external electrons

Total number of

atomic electrons n

59

60

61

62

63

64

65

66

67

Number in outermost

ring p

20

20

20

20

20

20

20

20

20

Number of electrons

16

16

16

17

17

17

17

17

17

in successive rings q ;

13

13

13

13

13

13

14

14

15

innermost ring at

8

8

9

9

10

10

10

10

10

the bottom

2

3

3

3

3

4

4

5

5

Adapted from J. J. Thomson,

Phil.

Mag. 7,

237 (1904).

PARTICLES AND QUANTA

307

ARCHIVE FOR THE HISTORY OF QUANTUM PHYSICS

Bohr's laboratory notebook at Manchester 1912. During one experiment he ran out of radon
and read a paper that launched him into the problem of atomic structure. Figure 5

ARCHIVE FOR THE HISTORY OF QUANTUM PHYSICS

Bohr's calculation ot the energy of an n-electron ring, from his “Manchester Memorandum " It
contains an error in the potential energy, and hence also in the total energy. Figure 6

are more like beads on a wire than like
freely orbiting particles.

There is no doubt that Bohr’s intro-
duction of the stability condition marked
a fundamental departure from Thomson’s
program. The form of the condition was
chosen in analogy to Max Planck’s quan-
tum theory, and with the expectation that
K might be a submultiple of Planck’s
constant h. It turned out that K = hi 2,
a fact Bohr discovered in February 1913,
when at last he came to examine Balmer’s
formula. The resulting account of the
Balmer lines and the concept of stationary
states forced him to conclude that the
frequencies of spectral lines are not the
mechanical frequencies of the atoms that
emit them.

As we now know, there followed a pro-
gressive relaxation of the dominion of
mechanics in the microphysical world,
culminating in the invention of quantum
mechanics and the principles of uncer-
tainty and complementarity. Nothing so
radical was in Bohr’s mind in June 1912,
however. Having taken a step that was to
have revolutionary consequences, he im-
mediately turned back to the problems of
the Thomsonian atomist.

In June or July of 1912 Bohr drew up
the notes now known as the “Manchester
Memorandum” for discussion with
Rutherford. The Memorandum opens
with a definition of the nuclear atom and
an acknowledgment of its mechanical in-
stability, which can be demonstrated, as
Bohr put it, “by an analysis similar to the
one used by Sir J. J. Thomson in his
t heory about the constitution of an atom.”
How then can one account for periodicity?
This was a pressing problem: No atomic
model unable to elucidate Mendeleev’s
table could decisively defeat Thom-
son’s.

Bohr thought he had a simple solution.
He computed the total energy W of each
electron in a ring of n electrons, and dis-
covered that W was negative for n < 7,
but positive for n > 7. Evidently for n >
7 the electrons leave the atom; for n < 7
they may be bound securely if their mo-
tions satisfy condition 1. For an atom
with more than seven electrons, several
rings will be required; but, in marked
contrast to Thomson’s model, the addi-
tional rings will be formed outside the
first, and the population of the outermost
will determine the valence of the atom.

“This,” said Bohr, “seems to offer a
very strong indication of a possible ex-
planation of the periodic law of the
chemical properties of the elements.”

An error

What is particularly interesting about
this analysis — other than the fact that it
addresses, as its first order of business,
Thomson’s central problem — is that it is
altogether wrong. Figure 6 shows Bohr’s
calculations. From the equation of mo-
tion, which is correct, it follows that T, the
kinetic energy of each electron, is Q/2r,

308

HISTORY OF PHYSICS

ARCHIVE FOR THE HISTORY OF QUANTUM PHYSICS

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The structures of simple molecules, according to Bohr’s Memorandum. The earliest useful ex-
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where Q = e2(n - An/ 4) and An =
SJLT’cscfrr i/n). (The balance of forces
makes mv2/r = Q/r2.) Bohr’s computa-
tion of the potential energy U is, however,
incorrect; because U belongs to both of
the interacting particles, the sum in
Bohr’s expression for U should be divided
by two. Then we have U = —Q/r and
W = U + T = —Q/2r = -T

The total energy is the negative of the
kinetic energy. Bohr’s error is the more
remarkable because his value for the po-
tential energy conflicts both with his
expression for the equation of motion and
with a theorem proved later in the Me-
morandum, namely that any particle
bound into an orbit by an inverse-square
force has a potential energy twice the
negative of its kinetic energy. Bohr’s slip
may betray his anxiety to solve Thom-
son’s problem of periodicity. (The sign of
W does change, but at a value of n > 500,
not 7 or 8 as Bohr wanted.)

For the rest, the Memorandum con-
cerns the structure of simple molecules
such as those illustrated in figure 7. Bohr
aimed to show, among other things, why
the H2 molecule occurs and He2 does not,
and to demonstrate that no charge is
transferred in the combination of identi-
cal atoms. He probably took the problem
of charge distribution in symmetric di-
atomic molecules from Thomson’s Cor-
puscular Theory of Matter, which gave
perhaps the earliest useful explanation of
chemical bonding via electron ex-
change.

Thomson had decided that charge
transfer occurs in the formation of H2 and
02 because identical plum-pudding atoms
can not remain in stable equilibrium. For
say they are symmetrically combined, by
interpenetration of their positive spheres;
any subsequent jostling would create a
flow of electrons from one sphere to the
other, and a permanent polar bond.
Thomson made this conclusion plausible
by a characteristic analogy. This system,
one of identical water-filled jars sus-
pended from identical springs and con-
nected with a siphon, is unstable; for any
relative vertical displacement of the jars
will grow with the flow of water through
the siphon. Thomson thought the evi-
dence favored asymmetric H2 and 02;
Bohr thought the case for symmetry
stronger; hence the considerable attention
given to the structure of simple molecules
in the Memorandum.

The second and third parts of Bohr’s
paper of 1913 remain within the set of
problems posed by the Memorandum.
Part II concerns the problem of the dis-
tribution of electrons into rings. Bohr
takes for granted the chief result of
Thomson’s program, the doctrine of
atomic number. He then lays down two
principles:

► In the ground state of an atom every
electron, regardless of its distance from
the nucleus, has just one quantum of an-
gular momentum.

► The ground-state configuration is the
one with the lowest possible potential
energy consistent with the principle of
angular momentum.

Alas! these directions do not suffice, for
they point to structures — such as a sin-
gle-ring lithium atom — in obvious dis-
agreement with atomic volumes and
chemical data. So Bohr assigned distri-
butions more by intuition than by prin-
ciple, with the curious result given in
Table 2. Note particularly the confluence
of inner rings at neon ( Z = 10) and argon
(Z = 18), brought about, Bohr thought, by
the demands of the usual laws of me-
chanics. Bohr’s care and trouble in con-
structing Table 2 may be indicated by the
alternative distributions of figure 8.

Part II of Bohr’s paper of 1913 also re-
solves— or rather shelves — the problem
of radioactivity by tucking it into the
nucleus. As for Part III, it argues the
merits of Bohr’s hydrogen molecules.

Thomson’s response

Thomson did not salute Bohr’s work as
the capstone of his own. To him, setting
down an arbitrary condition like T = Kv'
and pretending it had dynamical signifi-

cance, was not doing physics; it was a
screen of ignorance, a cowardly substitute
for “a knowledge of the structure of the
atom.” Nothing could be easier, or so
Thomson told the British Association for
the Advancement of Science in Septem-
ber 1913, than to obtain quantum theo-
retical results in an orthodox mechanical
manner.

Take Einstein’s formula for the pho-
toelectric effect, mv2/2 = hr, for example.
(For simplicity Thomson omitted the
work function.) Assume, he said, that the
usual Coulomb attraction A/r2 operates
only in a few separated, pie-shaped re-
gions in the atom and that, in addition, an
inverse-cube repulsion B/r 3 exists ev-
erywhere. An electron can sit in stable
equilibrium within the pie-shaped regions
at a distance a from the atom’s center,
where a = B/A. The frequency of small
vibrations about this position is

= /j_y/2

2ir a2 \mB/

Assume that a passing light wave of
frequency r = r' strikes the electron, and
gives it enough energy to cross from the
pie-shaped region into one of uncom-

Table 2. Bohr's electronic distribution, 1913

1(1)

7(4,3)

13(8,2,3)

19(8,8,2,1)

2(2)

8(4, 2, 2)

14(8,2,4)

20(8,8,2,2)

3(2,1)

9(4, 4,1)

15(8,4,3)

21(8,8,2,3)

4(2,2)

10(8,2)

16(8,4,2,2)

22(8,8,2,4)

5(2,3)

11(8,2,1)

17(8,4,4,1)

23(8,8,4,3)

6(2,4)

12(8,2,2)

18(8,8,2)

24(8,8,4,2,2)

From Phil. Mag. 26, 476 (1913). The symbol N(nx, n2, . . .) indicates the total number of
electrons and their distribution counting outward from the nucleus.

PARTICLES AND QUANTA

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X

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certain electronic parameters.

This tour de force was widely ap-
plauded by Thomson’s school. Nature

called it a “brilliant attempt” not soon to
be forgotten. Other sympathizers rushed
to reinterpret Bohr’s fundamental con-
tribution, the elucidation of the Balmer
lines. One likened the plum pudding to
a rotating, pulsating sphere of gas, and
imagined that the Balmer lines were
emitted by electrons running around on
nodal surfaces. Another made what he
called a “spherical counterpart” to
Thomson’s sectioned atom, a baroque
structure with many niches of stable
equilibrium about which an electron could

vibrate at one or another of the Balmer
frequencies.

Thomson himself contributed to this
curious literature. “If [the Bohr theory]
is true,” he said, “it must be the result of
forces whose existence has not been
demonstrated.” He set out to find these
forces, and to represent them in “the
working of a model”; and so, for a time, he
occupied himself in reinterpreting Bohr
— as Bohr had been reinterpreting him.
He ended by appealing to a force varying
sinusoidally with the distance between
the radiating electron and what he coyly
called the “positive center” of the atom.

These rearguard actions did nothing to
divert the progress of the quantum theory
of the atom. When academic physics
resumed after World War I, Thomson
recognized that he was out of date and
resigned the Cavendish professorship in
favor of Rutherford. Not that he gave up
physics; but he could never be persuaded
that quantum theory was a fundamental
one.

In his Recollections and Reflections , an
autobiography published in 1937,
Thomson allowed that Bohr’s papers had
“changed chaos into order” in certain
branches of spectroscopy. And that, he
thought, was “the most valuable contri-
bution which the quantum theory has
ever made to physical science.”

Further reading

• For Thomson: Dictionary of Scientific Bi-
ography, XIII, Scribners, New York (1976),
page 362; “The Scattering of a and (3 Parti-
cles and Rutherford’s Atom,” Archive for
History of Exact Science 4, 247 (1968).

• For Bohr: J. L. Heilbron, T. S. Kuhn, “The
Genesis of the Bohr Atom,” Historical
Studies in the Physical Sciences 1, 211
(1969).

• For the Archive for History of Quantum

Physics: T. S. Kuhn, J. L. Heilbron, P.
Forman, L. Allen, Sources for History of
Quantum Physics, American Philosophical
Society, Philadelphia (1967). □

310

HISTORY OF PHYSICS

60 YEARS of

QUANTUM PHYSICS

By Edward V. Condon PHYSICS TODAY / OCTOBER 1962

JWAS invited to speak on the occasion of the
1 500th Regular Meeting of the Society, and of
course am delighted to be able to come and do it.
But those who conveyed the invitation could not re-
frain from reminding me that I owed the Society a
retiring presidential address. I was president in 1951,
and it was in the fall of that year that I departed
hastily to go to Corning Glass Works to be director
of research. That was a very interesting experience,
and I am still connected with the glass business, though
I am also doing professing. I started my career in
experimental physics and lasted one day. When I
started work on a doctoral thesis at the University of
California in 1925 I had to set up a vacuum system.
All experimental physicists in those days had to get
a Cenco pump on the floor and glass tubing up to
something that was on the table. I started out like all
the rest but broke so much glass the first day that they
suggested I go into theoretical physics. I told this
story at Corning after I became their director of re-
search. Mr. Amory Houghton, chairman of the board,
who is now our ambassador to France, said, “Isn’t it
good that at last you are in a place where you can’t
possibly break enough glass to make any difference.”

Looking back over the various possibilities of things
that might be suitable to talk about this evening, I
thought it would be interesting to review the historical
development of what I now would like to call quan-
tum physics, rather than quantum mechanics, because
it has grown and expanded in such a way that it per-
meates all of modern physics. In fact it is extremely
difficult to think of any actively cultivated part of
physics that is not directly involved with Planck’s
quantum constant h. The basic discovery by Planck
was made within a week or two of exactly sixty years
ago, so I thought it might be interesting to discuss
this subject.

THE subject of quantum physics started with the
statistical theory of the distribution of energy in
the black-body spectrum. The spectrum of radiated
energy in equilibrium with matter in an enclosure is
commonly called black-body radiation because it is

the kind of radiation that would be emitted by a per-
fect absorber. The active problem in 1900 was the
explanation of the distribution of energy in the
spectrum.

It is interesting to realize that the subject has quite
an ancient history. The first application of thermo-
dynamics to black-body radiation goes back to 1859,
when Kirchhoff first developed the ideas of radiative
exchanges, and the connections between emission
and absorption, rules according to which a good emitter
is a good absorber, and a poor emitter is a poor ab-
sorber. In 1884 the discovery had been made of what
we now call the Stefan-Boltzmann law, that the total
radiation goes up as the fourth power of the absolute
temperature. It was discovered by Stefan experimen-
tally and interpreted theoretically by Boltzmann, mak-
ing it one of the earliest applications of thermodynam-
ics to radiation after those first ideas of Kirchhoff's.

In 1894 came the discovery by Wien of the dis-
placement law, which tells how the distribution of
energy over various wavelengths changes with the ab-
solute temperature. The big problem at that time was
to try to understand the reason for this distribution.
Contrary to the general belief, which has become true
in the last thirty years or so, that all physics is really

E. U. Condon is Wayman
Crow Professor of Physics
and head of the Department
of Physics at Washington
University in St. Louis, Mo.
He presented the address
upon which this article is
based on the occasion of the
1500th regular meeting of the
Philosophical Society of Wash-
ington, which was held on
December 2, 1960, at the

Natural History Museum Au-
ditorium of the Smithsonian
Institution in Washington,
D. C. His address is included
in Volume 16 of the archival
Bulletin of the Society.

PARTICLES AND QUANTA

311

Planck

Rayleigh

done by young men in their twenties, the discovery of
Planck was made when he was at the advanced age
of 42. In 1900 he had already put a part of his career
of research work behind him and was a professor in
the University of Berlin, so that his work on quantum
physics was done twenty-one years after he had re-
ceived his doctorate for a thesis on the second law of
thermodynamics. His thesis, it is interesting to note,
was done under Kirchhoff and Helmholtz at Berlin.
In his autobiography he says that he is quite confident
neither of them ever read it.

Thermodynamics was Planck’s first love, his prin-
cipal love throughout physics. In fact there are many
indications that he was rather annoyed with his dis-
covery of the Planck constant of action and did his
best for about fifteen years or so, on up to about
1915, to find ways of evading his own discovery and
reconciling the theory that he had discovered with
classical theory. This resembles somewhat the story
that I used to hear from Professor Ladenburg at
Princeton, about Roentgen. Everybody knows about
the great consequences of Roentgen’s discovery of the
Roentgen rays, or x rays. Ladenburg was a student
of Roentgen. He said that Roentgen was annoyed with
his x rays because he did not understand what they
were and much preferred classical subjects. So the
upshot of it was that Ladenburg did a doctoral thesis
under Roentgen just a few years after Roentgen had
discovered x rays, on the subject of the correction to
Stokes’ law for a body falling through a viscous
medium in a cylindrical tube, allowing for the finite
diameter of the tube and the wall effect. They had a
long pipe filled with castor oil, which is the traditional
viscous material. It reached from the top floor of the
laboratory to the basement. He said nothing ever gave
Roentgen quite as much pleasure as to see the steel
ball arrive down at the basement just when the calcu-
lation said it ought to. You can tell by a great deal of
Planck’s writings and readings that he felt much the
same way about classical physics in relation to the
modern developments.

Lord Rayleigh had published a theory, based on the
equipartition-of-energy doctrine that goes back to
Maxwell, Waterston, and Boltzmann, whereby every
degree of freedom in the radiation field should have
had the energy kT. He knew it did not, because that
would have given an infinite or divergent result. But
nevertheless that was where the theoretical thinking
of his time led, which served to point up the impor-
tance of the quantum modifications that had to be
made.

One of the things that I found interesting in look-
ing back in the history of this theory is that it has
always been referred to as the Rayleigh- Jeans law,
and I had supposed that Rayleigh and Jeans had
worked together on it. In point of fact, Rayleigh de-
rived it and made a mistake by a factor of 8, which
Jeans corrected in a letter to Nature, so that dividing
the original Rayleigh formula by 8 was Jeans’ con-
tribution.

It was an essential contribution because it is a mis-
take that we all might make very readily. In counting
up the degrees of freedom in the radiation field that
are associated with frequencies between v and v + dv,
one has to calculate how many integers there are whose
squares add up to a certain value, and it is natural to
take the volume of a sphere of a certain radius. But
in fact one takes only an octant out of this sphere
because the integers, all three of them, have to be
positive, and that is where Rayleigh went wrong.

The radiation measurements that served to inspire
Planck were being made at the Physikalisch-Tech-
nische Reichsanstalt by some of the great names of
early days of radiation-measurement work: Lummer,
Pringsheim, and Rubens. The problem of distribution
of energy in the spectrum was thus very much in the
foreground and very good measurements were being
made.

It was on October 19, 1900, that Planck presented
his radiation formula to the German Physical Society
at a meeting in Berlin, strictly as an empirical interpo-
lation formula between the Rayleigh- Jeans law, which

312

HISTORY OF PHYSICS

is valid at long wavelengths, and the Wien law,
which is valid at short wavelengths. By interpolating
in between, he had been able to find a simple formula
that extended across the whole region, but at that
time he had no theoretical basis for it whatever.

That night Rubens took the data to which he had
access and made a very careful comparison with
Planck’s formula — a more careful one than Planck
himself had made at that time — and found that it
represented the data with extraordinary accuracy,
much better than an empirical formula usually does.
He called on Planck the next morning with a strong
conviction that there was some real fundamental truth
in the formula and not just an accidental agreement.
Planck then set to work to find a theoretical basis for
this formula and worked very hard for quite a while.
In his autobiography he speaks of this as the most
difficult period of his whole life.

Then, within less than two months, on December 14,
1900 — so we are just twelve days ahead of the 60th
Anniversary — he presented a paper to the Physical
Society of Berlin in which he took the decisive step.
By applying the Boltzmann principle for the connection
of entropy with probability, which up to that time had
hardly been used at all, he was able to work out the
spectral distribution of energy that would be in equi-
librium with a system of electrical oscillators.

In order to get the desired result, he had to suppose
that the energy of each oscillator was built up in finite
steps of energy, whereas, in all of physics hitherto,
energy had been a continuous variable. To agree with
the Wien displacement law he then had to assume that
the finite size of these steps was proportional to the
frequency, and so the energy quanta were hv. In that
way he arrived at the famous formula, uv — [8?r/£3]
[hvs/(en,l/kT — 1)], for the density of the energy in
the spectral frequency range between v and v + dv in
black-body radiation at absolute temperature T. As is
readily seen, in the limit of hv/kT small compared with
1, this formula transforms into the Jeans formula; in
the limit of hv large compared with kT, it becomes
the Wien formula and represents the data with great
accuracy in between. Additional measurements of the
same sort, which were later made with great precision
at the National Bureau of Standards by W. W. Cob-
lentz, greatly improved our knowledge of the subject.

One of the most extraordinary aspects of this work
of Planck’s is the accuracy with which he was able to
define these fundamental constants. At that time there
was no good value available for Avogadro’s number,
or for the charge on the electron, and the values that
Planck was able to derive were much closer than is
usually appreciated. When he first represented the data,
in order to obtain a fit with the old black-body data,
he had to assume that li was 6.885 X KT27 erg -sec,
and that k, which we now call the Boltzmann constant,
was 1.429 X l(Yle erg/°K. The present best value for
first number is 6.6252 X 10-27, instead of 6.885 X
10-27; and for the second number, it is 1.3804 X 10~16,
instead of 1.429 X IQ-10. At that very first time Planck

got Planck’s constant only about 4.4 percent too high,
and Boltzmann’s constant about 3.5 percent too high,
relative to the best modern values.

This was actually the first time that the Boltzmann
constant had been evaluated. Let me just remind you
of its relation to the other basic constants that have
so much importance.

The gas constant, R, as we ordinarily know it, per
gram mole, is equal to the Avogadro number, N, times
k; and the Faraday, F, the amount of charge needed
to plate out a gram mole of univalent ions, is equal
to Avogadro’s constant times the charge of the elec-
tron. That is, R = Nk, and F = Ne.

These molar quantities, R and F, were well known,
and good values for them were available in those days,
but what was not known was the Avogadro number N.
However, if you know any one of these quantities you
can get the other, so, as it turns out, obtaining the
Boltzmann constant, k, enables one to get N by the
first equation, and then, by using that N in combina-
tion with the knowledge of the Faraday, F, one is able
to get the charge on the electron.

The electron had only been recognized about three
years earlier by J. J. Thomson, and while the ratio of
its charge to mass was known, its charge by itself was
not well known. You will find, in the literature of
that time, values published for e, the charge on the
electron, ranging all the way from 1.29 X 10-10 elec-
trostatic units, on up to 6.5 X 10~10 electrostatic units,
which was given by J. J. Thomson, and a little while
later revised back down to 3.4 X KT10. In other words
at that time one only knew the charge on the electron
to a factor of about 5 or 6.

On the other hand if you take the value of the Fara-
day and the value of k and solve for N from the gas
constant and then solve for e, you find, surprisingly
enough, that e equals 4.69 X 10~10 electrostatic units,
which is only 2.3 percent below the currently recog-
nized value.

Thus, in the space of just a month or two, Planck
first found an empirical formula which to this day
gives the most accurate representation of the spectral
distribution of the radiant energy; second, he found
a derivation of that formula. In order to get the deri-
vation he had to introduce the extraordinary idea of
energy quantization into physics. Third, he obtained
an excellent value for the charge on the electron, which
everybody was trying to do at that time.

You might expect that this would cause a great
deal of excitement among physicists at that time, but
it did not. If you search through the journals you find
practically nothing is said about Planck in the years
1900 through 1904. I was very much intrigued, there-
fore, when just before this meeting Mr. Marton re-
called that a search of the records of this Society
indicated that in 1902 Arthur L. Day gave a report
on Planck’s work. Thus, The Philosophical Society of
Washington was one of the earliest to pay attention
to it.

The first real extension of Planck’s work came with

PARTICLES AND QUANTA

313

Einstein’s famous paper of 190S, the paper for which
he got the Nobel Prize. (It is important to realize that
Einstein did not get the Nobel Prize for the theory of
relativity. They might give it to him now if he were
around, but they did not in those days.) Planck wrote
only one other paper on the subject in that period be-
tween 1900 and 1905 and this was mainly an exposi-
tory paper. There is one brief mention by Burbury,
another paper by van der Waals, Jr., and that is all.
In those days Planck was almost completely ignored.

In Planck’s own autobiography he tells of his own
attitude toward the Planck constant, and I thought it
would be interesting to read his own words on that,
of course translated into English. He said:

While the significance of the quantum of action for
the interrelation between entropy and probability was
thus conclusively established, the great part played by
this new constant in the uniform regular occurrence
of physical processes still remained an open question.

I therefore tried immediately to weld the elementary
quantum of action, h, somehow into the framework
of classical theory. But in the face of all such attempts
the constant showed itself to be obdurate.

So long as it could be regarded as infinitesimally
small, i.e., when dealing with higher energies and
longer periods of time, everything was in perfect order.
But in the general case difficulties would arise at one
point or another, difficulties which became more
noticeable as higher frequencies were taken into con-
sideration. The failure of every attempt to bridge that
obstacle soon made it evident that the elementary
quantum of action plays a fundamental part in atomic
physics and that its introduction opened up a new era
in natural science, for it heralded the advent of some-
thing entirely unprecedented and was destined to re-
model basically the physical outlook and thinking
of man which, ever since Leibniz and Newton laid
the ground work for infinitesimal calculus, were
founded on the assumption that all causal interactions
are continuous.

He goes on in a more personal vein to say:

My futile attempts to fit the elementary quantum
of action somehow into the classical theory continued
for a number of years [actually until 1915] and they
cost me a great deal of effort. Many of my colleagues
saw in this something bordering on a tragedy. But
I feel differently about it, for the thorough enlighten-
ment I thus received was all the more valuable. I
now knew for a fact that the elementary quantum of
action played a far more significant part in physics
than I had originally been inclined to suspect, and
this recognition made me see clearly the need for the
introduction of totally new methods of analysis and
reasoning in the treatment of atomic problems.

In spite of Jeans’ intimate association with this
problem, you find no reference whatever to the Planck
black-body law in the first edition of his Dynamical
Theory of Gases, which was published in 1904, four
years after Planck’s work. In the Landolt-Bornstein
Tables, published in 1905, we find an extraordinary
thing, namely, that it gives widely different values for
what is often called the Loschmidt number, the num-

ber of molecules in one cubic centimeter of various
gases under standard conditions. Of course this value
should be the same for all gases. But they solemnly
give you a table with 2.1 X 1019 for air, 4.2 X 1019
for nitrogen, 7.3 X 1019 for hydrogen, and so on.
Apparently Landolt and Bornstein did not believe in
the Avogadro number. Planck got 2.76 X 1019 for this
number, which as we have seen is a good value.

Josiah Willard Gibbs was America’s first great theo-
retical physicist. He was elected, I find, to member-
ship in the Washington Academy of Sciences in 1900.
He died in 1903 at the age of 64. There is no indication
in any of his publications or notes that he left behind
that he paid any attention to Planck’s work. He had
puzzled over the problem of the specific heat of poly-
atomic gases, which everybody was puzzled about at
that time, because it has too low a value to correspond
with the equipartition law. There is some indication
that he found these difficulties with the equipartition
law revealed in the specific heat of gases somewhat
depressing, and I find an indication of that, perhaps,
in an interesting paragraph from the preface to his
famous work on statistical mechanics, published in
1902, a year before Gibbs’ death:

In the present state of science it seems hardly pos-
sible to frame a dynamic theory of molecular action
which shall embrace the phenomena of thermodynam-
ics, of radiation and of the electrical manifestations
which accompany the union of atoms. Yet any theory
is obviously inadequate that does not take account
of all these phenomena. [Then comes a wonderful sen-
tence at the end of this paragraph which I think we
all ought to realize was written by Gibbs in 1902:]
Certainly one is building on an insecure foundation
who rests his work on hypotheses concerning the con-
stitution of matter.

Lord Kelvin’s Baltimore lectures, which were deliv-
ered at The Johns Hopkins University in 1884 but
were not published until 1904, had undergone a great
deal of revision up to the latter date. The preface to
these lectures is very interesting to those who have
anything to do with editing or getting things through
the press. He admits that he had been working on the
revision for all of the nineteen years. I can well im-
agine that he was a popular fellow around the print
shop.

That work includes as its appendix B, the famous
lecture to which I am sure you have all heard allu-
sions, “Nineteenth Century Clouds over the Dynami-
cal Theory of Heat and Light.” That lecture was de-
livered in April 1900, some months before Planck’s
work, and then it was published originally in the Philo-
sophical Magazine of July 1901. It makes no reference
to the black-body radiation or to Planck’s work, al-
though cloud 2 — he had his clouds numbered — was this
same concern about the failure of equipartition of en-
ergy as evidenced by the specific heats of gases, the
same problem that was troubling Gibbs.

Lord Rayleigh’s publication of what we now call the
Rayleigh- Jeans law was in the Philosophical Magazine

HISTORY OF PHYSICS

in 1900. He did not return to the subject again until
190S when he wrote several notes in Nature in which
he concedes or agrees with the comment that Jeans
had made about being wrong by a factor of 8. It is
interesting in that he says that he “has not succeeded
in following Planck’s reasoning”. That is how Planck’s
work was received by Lord Rayleigh, one of the great-
est British physicists. Rayleigh actually published
papers actively through 1919, but he seems to have had
no more to say on black-body radiation than what he
said in that one 190S paper.

Search through his published papers reveals two more
items relating to modern quantum physics. In the 1906
Philosophical Magazine he comments on the classical
radiative properties of the atom models that resemble
J. J. Thomson’s. However, he goes beyond them in
that he regards the negative charge as distributed more
like a continuous fluid and studies it as a normal mode-
of-vibration problem. In an editorial note added to
his collected papers, written in 1911, he refers back
to some old work of an 1897 paper. An interesting
thing to me is his comment that all kinds of models
of normal modes of vibrations of continuous systems
always lead to formulas in which the square of the
frequency is written additively as the sum of contri-
butions coming from the different degrees of freedom
— from what we would now call the different quantum
numbers. Rayleigh was wedded to a classical vibration-
theory model where the squares of the frequencies get
in because of the second derivative with regard to
the time, based on Newton’s law of mechanics. Nowa-
days, when we lecture on quantum mechanics, we just
quietly make the Schrodinger equation contain the
first time derivative so we will not have this trouble,
which is the advantage of making up your equations
as you go along as compared with getting them from
someone like Newton.

Steeped in acoustics as he was, Rayleigh does say:
“A partial escape from these difficulties might be found
in regarding the actual spectrum lines as due to differ-
ence tones from primaries of much higher pitch.” That
is a well-known device giving physicists license to pass
from a square term to a linear term; that is, a small
change in the square is linear.

There is still something else in the 1906 paper which
intrigues me. Rayleigh devotes a paragraph to the
problem of the sharpness of spectral lines despite the
random character of the conditions of excitation, and
concludes with a paragraph that sounds very modern.
I quote:

It is possible, however, that the conditions of sta-
bility or of exemption from radiation may, after all,
demand this definiteness, notwithstanding that in the
comparatively simple cases treated by Thomson, the
angular velocity is open to variation. According to
this view, the frequencies observed in the spectrum
may not be frequencies of disturbance or of oscilla-
tion in the ordinary sense at all, but rather form an
essential part of the original constitution of the atom
as determined by conditions of stability.

Maybe one reads into the statement one’s present
knowledge of the later developments of quantum the-
ory, but I found it very interesting as a foreshadowing
of the way we look at it now.

Even as late as 1911, we find Lord Rayleigh worry-
ing about Kelvin’s cloud 2, the specific-heat difficulty,
although Einstein had really put that difficulty to rest
in 1907. In 1911, Rayleigh wrote to Walter Nernst to
express his concern:

If we begin by supposing an elastic body to be
rather stiff, the vibrations have their full share of kin-
etic energy [that is the equipartition law] and this
share cannot be diminished by increasing the stiff-
ness. . . .

We all know that increasing the stiffness makes the
interval between the vibration quantum levels greater,
so that they do not take part practically in the equi-
partition law simply because they cannot get enough
energy even to be excited to the first state.

However, Rayleigh goes on:

Perhaps this failure might be invoked in support
of the views of Planck and his school that the laws
of dynamics as hitherto understood cannot be applied
to the smallest part of the bodies. But I must confess
that I do not like this solution of the puzzle ... I
have a difficulty in accepting it as a picture of what
actually takes place.

We do well I think to concentrate attention on the
diatomic gaseous molecule. Under the influence of col-
lisions the molecule freely and rapidly acquires rota-
tion. [He knows this from the specific heat.] Why
does it not also acquire vibration along the line joining
the two atoms?

If I rightly understand the answer of Planck is that
in consideration of the stiffness of the union, the
amount of energy that should be acquired at each
collision falls below the minimum possible and that
therefore none at all is acquired [this is of course
exactly what we know] an argument which certainly
sounds paradoxical.

This is the end of it for Rayleigh.

So we can see that the acceptance of these ideas was
something that came very, very slowly. The examples
I have chosen illustrate that very little was stated
about the subject at all from 1900 to 1905, and even
after that you find the great men of the period hesitant
and unwilling to build it into their thinking.

T ET us now turn to Einstein’s famous 1905 paper,
■*— 1 which I must confess I had not read until I got
to thinking over the preparation for this lecture. It is
one of the papers we all hear about in school and wor-
ship, but do not read. One of the odd things about this
paper is that “h” is not in it, believe it or not. In the
paper Einstein denotes by the letter (3 what we now
would call h/k, and then he writes R/N for what we
call k, and thus you find in that paper that the energy
of a light quantum is not hv at all. It is RPv/N, which
certainly takes a bit of getting used to.

The title of his paper is an interesting one: “Heuris-

PARTICLES AND QUANTA

315

tic Viewpoint Concerning the Emission and Trans-
formation of Light”, indicating, I think, that he meant
that there is something in the paper, but he does not
quite know what. At least that is what I mean when
I say “heuristic”. Einstein might, of course, have
meant something else. He says:

The energy of a ponderable body cannot be divided
into indefinitely many indefinitely small parts, whereas
the energy emitted by a point light source is regarded
on the Maxwell theory or more generally according to
every wave theory as continuously spread over a con-
tinuously increasing volume.

Such wave theories of light have given a good repre-
sentation of purely optical phenomena and will surely
not be replaced by any other theory. [He was right
in that. They have not been replaced.]

He continues:

It is to be remembered, however, that the optical
observations referred to time mean values, not to in-
stantaneous values, and it is quite conceivable that,
in spite of complete success in dealing with diffraction,
reflection, refraction, dispersion, et cetefa, such a the-
ory of continuous fields could lead to contradictions
with experience when applied to phenomena of light
emission and absorption.

After a little more discussion he makes the key
declaration that played such a decisive role in all
subsequent developments in which, in one sentence,
he says :

According to the supposition here considered, the
energy in the light propagated from rays from a point
is not smeared out continuously over larger and larger
volumes, but rather consists of a finite number of
energy quanta localized at space points, which move
without breaking up and which can be absorbed or
emitted only as wholes.

Oddly enough, though nowadays this paper is quoted
purely for the photoelectric effect in the discussion, the
photoelectric effect is only one section, paragraph 8,
of the whole paper. The first six paragraphs are con-
cerned entirely with another way of looking at the
details of the statistical distribution of the black-body
radiation law, and the entropy of radiation along the
lines of the quantized wave theory.

Finally, paragraph 7 is an interpretation of the
Stokes’ rules for photoluminescence. In ordinary fluo-
rescence and phosphorescence, Stokes’ law, which goes
way back to 1860, says that the wavelength of the
fluorescent light is always greater than the wavelength
of the exciting light, or nearly so. There is some radia-
tion, called anti-Stokes radiation, for which the wave-
length is a little shorter.

Why there was so little stress in Einstein’s paper
on the photoelectric effect, compared with these other
things, puzzled me. Then I came to section 8, which
deals with the photoelectric effect, and I asked Pro-
fessor A. L. Hughes, one of the pioneers of photo-
electric work, who is at our place — he is emeritus
professor in Washington University in St. Louis — how

that could be. He told me how very primitive the
knowledge of the photoelectric effect was at that time.
No vacuum work on photoelectricity had been done,
and, even if it had, it would have been done with very
poor vacuums, under very poor conditions. In point of
fact, no effort had been made to determine the retard-
ing potential required to stop the photocurrent in a
definite circuit.

What had been observed was that, if you insulate
a metal object and shine light on it, it will build up
to a certain potential and then stay at that potential.
That is, it builds up its own retarding potential and
finally prevents the escape of further electrons into
the air. Metals differ with regard to the potential built
up by certain kinds of light, and it was found that as
one went to more and more violet light one got a
higher potential. But these were only very crude meas-
urements indeed, so crude that one would hardly think
that they might offer any possibility of fundamental
understanding.

That, perhaps, is the reason why the photoelectric
effect was so little stressed in Einstein’s paper. The
Stokes’-law argument was much more directly experi-
mental, and, conversely, it seems rather odd to me, as
I think about it, that Stokes’ law is not more stressed
today in teaching the subject.

It was in 1907 that the specific-heat work of Ein-
stein clarified the problem of low-temperature specific
heat.

It is fascinating to look up some of the historical
information that is available in the literature. I do
not mean that one has to go to ancient history, just
the history of the last century. For example, in 1904,
when the great St. Louis World’s Fair was held, vari-
ous distinguished visitors presented lectures. Lord Kel-
vin gave a speech suggestive of a sort of inverse neu-
trino theory. The thing bothering him at that time
was — this is a little off the subject of quantum theory,
but I think it is interesting — the measurement that had
just been made by the Curies of the amount of energy
given off by radium per unit time. They had not
measured the half life, and the energy given off did
not show any signs of weakening, and you know that
physicists are great on extrapolation. They said that
radium gives off energy perpetually — that was the
word, perpetually.

So the question was, how could anything radiate
perpetually at this tremendous rate? — a rate unheard
of when expressed in terms of energies of usual chemi-
cal reactions.

Kelvin had an idea which he propounded at this
talk; perhaps, he suggested, there was some kind of
energy that one could not detect — like the neutrinos —
floating around in space, and perhaps radium had the
property of absorbing it in that form and then recon-
verting it, like a fountain, and shooting it out, and
that was what was observed. Even in those days,
people were perfectly willing to balance the books on
conservation of energy in such a manner.

HISTORY OF PHYSICS

J. J. Thomson

the young Bohr

THE next major historical event was the develop-
ment of the Bohr atom model in 1913. At this
point, since we are just talking a little bit of anecdotal
material about the history of our subject, I will tell
a story that I learned from George Gamow. The young
Bohr — he was about 26 at that time — came to Eng-
land from Copenhagen to work in the Cavendish Labo-
ratory. The great J. J. Thomson was at the height of
his powers. Bohr came to the great center to study
fundamental atomic physics, but within a few months
he left the Cavendish Laboratory and went up to Man-
chester to work under a relatively unknown fellow
named Rutherford. The question is, why did he do
that? According to Gamow, Bohr had gotten into
trouble with “J. J.” because he was a little critical of
the Thomson atom model, and “J. J.” had politely indi-
cated to him that it might be nice if he left Cambridge
and went to work with Rutherford. That is how Bohr
went to work for Rutherford, which was advantageous,
I think, for all. It was not so good for the Thomson
model but it was fine for the future development of
physics.

To bring this story up to date, Gamow told me that
in 1928, when he worked on the alpha-particle tunnel-
ing paper, the basic work which Gurney and I did
simultaneously in Princeton, Rutherford sent Gamow
to see Bohr and to tell him about this exciting new
development. He also wrote him a letter — of which
Gamow said he still has a copy— saying, “Please pay
attention to this fellow; there is something in it. It
isn’t cockeyed. You remember how it was with you
when you went to ‘J. J.’ and he wouldn’t listen ; so now
you listen to Gamow.” I do not know whether there

is any truth in that or not, but at any rate Bohr did
listen to Gamow.

Of course the most exciting immediate experimental
consequence of Bohr’s work, besides the direct inter-
pretation of the spectrum of hydrogen which was well
known at that time (I mean the facts of the Balmer
series, which went way back into the 19th century),
was the interpretation of spectroscopic-term values as
being energy levels with the associated implication that
controlled electron impact would produce controlled
excitation of atoms and molecules. This was the work
that was immediately carried further by James Franck
and Gustav Hertz, and for which they received the
Nobel Prize in 1926.

That work was very quickly taken up here in Wash-
ington, in the pioneer work of Paul Foote and F. L.
Mohler. At the Bureau of Standards the accountants
were rather stuffy, and had rather sharp lines about
appropriations and budgets, so all the work on critical
potentials for which the Bureau became famous was
carried on under a budget number which had something
to do with improving pyrometric methods. I am not
sure it helped much in advancing pyrometry, but it
certainly was a great addition to the development of
science.

The period of the second decade of our subject was
also characterized by the very first extension of the
idea of quantized energy levels to the interpretation of
band spectra, rotation and vibration spectra, and
infrared.

A curious thing about the atom-model work of Bohr,
prior to 1923 or 1924, was that if you look at the then-
current papers you get the impression that everybody

PARTICLES AND QUANTA

Born Heisenberg

in the world was terrifically excited about the Bohr
model and believed in it hook, line, and sinker, includ-
ing the electron orbits as they are used in the ads for
the atomic age nowadays. Bohr, on the other hand,
was constantly making remarks, speeches, and admoni-
tions to the effect that this is temporary and we ought
to be looking for a way to do it right.

THE great breakthrough, as the modern saying
goes, came about in 1924, 1925, and 1926, when
the idea of waves accompanying electrons was first
published by de Broglie as a doctor’s thesis — and was
also ignored. I do not know anybody who read that
paper until a year or two later. Schrodinger then
founded the great discoveries of wave mechanics on
de Broglie’s work in the series published in the spring
of 1926.

Just before Schrodinger’s work in late 1925, Born,
Jordan, and Heisenberg had developed the matrix-
mechanics methods. For about a year they were
thought of as two rival and distinct theories, until
Schrodinger and Carl Eckart, then a young physicist
in Chicago, who is now in La Jolla, recognized the
mathematical identity of the two theories.

I had the good fortune to get my doctorate in the
summer of 1926 when all these things were at their
highest peak of excitement, and went to Gottingen to

work with Born. There was a young graduate student
there named Robert Oppenheimer with whom I got
acquainted at that time.

It was an extremely difficult period because the rate
of advance was so great, and the whole subject was so
obscure to all of us, that it was hard to keep up with
the state of affairs. I remember that David Hilbert was
lecturing on quantum theory that fall, although he
was in very poor health at the time. (He had anemia,
and liver extract was then unavailable, so he was eat-
ing a vast quantity of liver every day and saying he
would rather not live than eat that much liver. His life
was saved by the fact that liver extract was discovered
just about that time.) But that is not the point of my
story. What I was going to say is that Hilbert was
having a great laugh on Born and Heisenberg and the
Gottingen theoretical physicists because when they
first discovered matrix mechanics they were having, of
course, the same kind of trouble that everybody else
had in trying to solve problems and to manipulate and
really do things with matrices. So they went to Hilbert
for help, and Hilbert said the only times that he had
ever had anything to do with matrices was when they
came up as a sort of by-product of the eigenvalues of
the boundary-value problem of a differential equation.
So if you look for the differential equation which has
these matrices you can probably do more with that.
They had thought it was a goofy idea and that Hilbert
did not know what he was talking about, so he was
having a lot of fun pointing out to them that they
could have discovered Schrodinger’s wave mechanics
six months earlier if they had paid a little more atten-
tion to him.

I mention some of the occurrences of those years
because I do not believe that anybody who did not
live through that period can fully appreciate what a
tremendous number of things happened then that are
still very basic, and have blossomed out into whole
areas of physics which now are subjects for courses
in themselves.

In 1926 we had the whole wave mechanics, as we
know it, and the whole matrix mechanics formulated,
And just a little before that, we had the discovery of
the electron spin and of the Pauli exclusion principle.
In 1927 came the whole theory of the chemical valence
bond as a perturbation problem in quantum mechanics,
with correlations over electron pairs with their spins
antiparallel. Almost simultaneously, there occurred the
whole development of Fermi-Dirac statistics and its
clarification of the problems of metal theory. A few
months later, the Dirac papers on the quantization of
the electromagnetic field explained, at last, the differ-
ence between spontaneous and induced emission and
put the two together in a unified theory. Soon after
that came the whole Dirac relativistic theory of the
electron, which later led to the prediction of the posi-
tron.

Shortly thereafter, in 1928, the interpretation of
natural alpha radioactivity came as a consequence
of the barrier-leakage idea, also an essential element of

317

318

HISTORY OF PHYSICS

quantum mechanics and an essential element of its
statistical or probability interpretation. I think it is
fair to say that the barrier-leakage idea was the open-
ing of the modern period of the application of quantum
mechanics to nuclear physics. Nuclear physics, in terms
of real specific models, has never had a classical past.
Nobody tried in those days to develop specific models
of the structure of a nucleus.

Another big year for discoveries was 1932, the year
in which Urey discovered heavy hydrogen, which from
a nuclear point of view means the deuteron, the year
in which the first production of an artificial nuclear re-
action was accomplished by Cockcroft and Walton, the
year in which the positron was discovered — the anti-
particle associated with the electron, as we call it nowa-
days, and the year in which the neutron was discovered.

In that same decade, a few years later, 1936 saw the
development of the Fermi theory of beta decay based
on the neutrino hypothesis that had been introduced
by Pauli, in almost a joking way, a year or two earlier.

I remember that in the summer of 1937, when we
had a conference on beta-decay theory at Cornell Uni-
versity, and a lot of us were having trouble worrying
about it, Fermi was in the audience sitting in the back
row just smiling and smiling as he usually did. People
tried to get him to comment, and he said, “I have
always been surprised that people take that theory
so seriously.” But, as we know, it has turned out to
be remarkably correct — that is, the basic formalism
which Fermi developed then for accounting for the
four-fermion interactions, even in spite of the great
crisis it went through in 1957 with the discovery of
nonconservation of parity. The basic formalism, as
Fermi first introduced it, has beautifully stood the
test of time.

The year 1936 is also important to us here because of
work done by prominent people in Washington. I refer
to the work of Hafstad, Heidenberg, and Tuve in the
first real studies of proton-proton scattering, which
gave direct evidence of forces between protons other
than the Coulomb forces, that is, short-range nuclear
forces between protons. The theoretical interpretations
of those results were largely done in Princeton by
Gregory Breit and myself, in association with Richard
Present, who is now at the University of Tennessee.
That provided the first evidence of what is now called
the charge independence of nuclear forces, because
the additional short-range force that was revealed in
this way turned out quantitatively to be very close to
the force between a proton and a neutron which is
revealed in the normal state of the deuteron.

From about 1932 on, the whole field of nuclear
physics came into being in a big way, with deuterons
available and with machines available, both cyclotrons
and Van de Graaff machines. In the latter part of that
decade, we began to have the first theories of Bethe
and Marshak on the application of specific models of
nuclear reactions to the problem of finding satisfactory
sources of stellar energy.

I THINK perhaps I must give up at this point,
because the last two decades have seen such an
overwhelmingly rapid and vast amount of progress,
spreading out into so great many different fields, that
one could not possibly, in the short time remaining,
do more than just mention it.

We had, in the decade from 1940 to 1950, the whole
development of the modern point of view on quantum
electrodynamics. It came rather late in the decade,
with the discovery of the Lamb shift and the experi-
mental confirmation of the abnormal magnetic moment
of the electron, which was somewhat off from the
original Dirac theory. We had at last the clarification
of the puzzling features of the mesons in cosmic rays,
whereby it turned out that there were the two kinds,
the pi mesons and the mu mesons, the pi mesons de-
caying into the mu mesons. The latter part of the
decade represented the beginning of public knowledge
of fission, and the engineering and political uses of
fission.

At the same time, going off in quite another direc-
tion, what has turned out to be of equal importance
has been the whole wide development of the applica-
tion of Fermi statistics to electrons in solids, first re-
sulting in the major classification of properties of
metals, then of semiconductors, and then finally of
really modern tailored effects that led to transistors
and other devices.

The decade just passed has corresponded to an
enormous further development along these same lines.
We have the study of nuclear reactions going on up
to higher energies of some hundreds of millions of
volts, with predominant interest in the study of polari-
zation effects in nuclear reactions as another way of
getting at points of detail; the recognition of the non-
conservation of parity; the experimental discovery of
the neutrino; the recognition that the Fermi inter-
action that applies in weak interactions is more general
than simply the beta decay, applying also to muon
decay and other related processes; and the discovery
of the strange particles.

And then finally, as a roundup of mentioning things
that we do not have time to talk about, there are the
extraordinarily fine extensions that have been made in
the last five years of the theory of broad, modern,
good perturbation-theory methods for dealing with the
many-body problem. They involved not only the better
calculation of nuclear models but also, at last, after
many years of effort, they are beginning to provide
a real understanding of superfluids.

I want to close by remarking that all this started,
as I said, almost exactly 60 years ago — barring two
weeks — on December 14, 1900, when Planck’s constant
was first introduced into physics. In the 60 years that
have intervened it is now almost impossible to find
many papers in physics which do not deal directly or
indirectly with phenomena that are fully and basically
conditioned by the existence of that one universal
constant.

PARTICLES AND QUANTA

319

REMINISCENCES OF

Heisenberg and the early days
of quantum mechanics

Recollections of the days, 50 years ago, when a handful of students
in the “entirely useless” field of physics heard of a strange new mechanics
invented by Maurice de Broglie, Werner Heisenberg and Erwin Schrodinger.

Felix Bloch

It is appropriate in this year, when we
celebrate the 50th anniversary of quan-
tum mechanics, and during which we have
been saddened by the death of one of its
leading founders, Werner Heisenberg, to
reminisce about the formative years of the
new mechanics. At the time when the
foundations of physics were being re-
placed with totally new concepts I was a
student of physics. I sat in the collo-
quium audience when Peter Debye made
the suggestions to Erwin Schrodinger that
started him on the study of de Broglie
waves and the search for their wave
equation. It was from Heisenberg, as his
first doctorate student, that I caught the
spirit of research, and that I received the
encouragement to make my own contri-
butions.

First inklings

Let me begin by going back to 1924,
when I entered the Swiss Federal Insti-
tute of Technology in my home town of
Zurich. I began as a student of engi-
neering but after a year and good deal of
soul searching I decided, against all good
sense, to switch over to the “entirely use-
less" field of physics. The E. T. H., as it
is known from its German name, was an
institution of great international repute
and in my newly chosen field of studies I
had heard of such famous men as Peter
Debye and Hermann Weyl. In fact, the
first introductory course of physics I took
was taught by Debye and, without know-
ing much about his scientific work, I re-
alized from the high quality of his lectures
at the Institute that here was a great
master of his field.

There was a good deal less to be en-
thusiastic about in the other courses one

Felix Bloch, winner (with E. M. Purcell) of the
1952 Nobel Prize in physics, is professor
emeritus of physics at Stanford University.

could take, and there was nothing like the
complete menu that is presented to the
students nowadays. Once in a while, a
professor would offer a special course on
a subject he just happened to be inter-
ested in, completely disregarding the
tremendous gaps in our knowledge left by
this system. Anyway, there was only a
handful of us foolish enough to study
physics and it was evidently not thought
worthwhile to bother much about these
“odd fellows.” The only thing we could
do about it was to go to the library and
read some books, although nobody would
advise us which ones to choose.

Among the first I hit upon was Arnold
Sommerfeld’s Atomic Structure and
Spectral Lines, which I found fascinating;
the only trouble was that I could not un-
derstand most of it because I knew far too
little of mechanics and electrodynamics.
So at first I had to learn about these
subjects from other books, to truly ap-
preciate what Sommerfeld said; but then
it conveyed the good feeling that every-
thing about atoms was completely known
and understood. The fact that one really
could handle only periodic systems and
only those that allowed a separation of
variables did not seem a great cause for
concern. Therefore, when I saw a paper
in which somebody tried to squeeze the
theory of the Compton Effect into that
scheme, I was more impressed than dis-
couraged by the complicated mathematics
spent in the effort.

The news that the foundations of a new
mechanics had already been laid by
Maurice de Broglie and Heisenberg had
hardly leaked to Zurich yet and certainly
had not penetrated to our lower strata.
The first inklings of such a thing came to
me in early 1926; I had by then started to
attend the physics colloquium regularly,
although most of what I heard there was
far above my head. The colloquium, run

PHYSICS TODAY / DECEMBER 1976

with firm authority by Debye, might have
had an audience of as much as a couple of
dozen — on a good day.

Physics was also taught at the Univer-
sity of Zurich by a smaller and rather less
illustrious faculty than that at the E. T. H.
Theory there was in the hands of a certain
Austrian of the name of Schrodinger, and
the colloquium was alternately held at
both institutions. I apologize to my
friends who already have heard from me
what I am going to tell you now. My ac-
count may not conform to the strictest
standards of history, which accord valid-
ity only to written documents, nor will I
be able to render the exact words I heard
on those occasions, but I can vouchsafe
that, in content, I shall report the truth
and only the truth.

A wave equation is found

Once at the end of a colloquium I heard
Debye saying something like: “Schro-
dinger, you are not working right now on
very important problems anyway. Why
don’t you tell us some time about that
thesis of de Broglie, which seems to have
attracted some attention.”

So, in one of the next colloquia, Schro-
dinger gave a beautifully clear account of
how de Broglie associated a wave with a
particle and how he could obtain the
quantization rules of Niels Bohr and
Sommerfeld by demanding that an inte-
ger number of waves should be fitted
along a stationary orbit. When he had
finished, Debye casually remarked that he
thought this way of talking was rather
childish. As a student of Sommerfeld he
had learned that, to deal properly with
waves, one had to have a wave equation.
It sounded quite trivial and did not seem
to make a great impression, but Schro-
dinger evidently thought a bit more about
the idea afterwards.

Just a few weeks later he gave another

320

HISTORY OF PHYSICS

HEISENBERG

talk in the colloquium which he started by
saying: “My colleague Debye suggested
that one should have a wave equation;
well, I have found one!”

And then he told us essentially what he
was about to publish under the title
“Quantization as Eigenvalue Problem” as
a first paper of a series in the Annalen der
Physik. I was still too green to really
appreciate the significance of this talk,
but from the general reaction of the au-
dience I realized that something rather
important had happened, and I need not
tell you what the name of Schrodinger has
meant from then on. Many years later,
I reminded Debye of his remark about the
wave equation; interestingly enough he
claimed that he had forgotten about it and
I am not quite sure whether this was not
the subconscious suppression of his regret
that he had not done it himself. In any
event, he turned to me with a broad smile
and said: “Well, wasn’t I right?”

Of course, there was afterwards a lot of
talk among the physicists of Zurich, in-
cluding even the students, about that
mysterious “psi” of Schrodinger. In the
summer of 1926, a fine little conference
was held there and at the end everyone
joined a boat trip to dinner in a restaurant
on the lake. As a young Privatdozent,
Erich Hiickel worked at that time on what
is now well known as the Debye-Hiickel
theory of strong electrolytes, and on the
occasion he incited and helped us to
compose some verses, which did not show
too much respect for the great professors.
As an example, I wan}, to quote the one on
Erwin Schrodinger in its original Ger-
man:

“Gar Manches rechnet Erwin schon

Mit seiner Wellenfunktion.

Nur wissen moeht’ man gerne wohl

Was man sich dabei vorstell'n soil.’’

In free translation:

Erwin with his psi can do

Calculations quite a few.

But one thing has not been seen:

Just what does psi really mean?

Well, the trouble was that Schrodinger
did not know it himself. Max Born’s in-
terpretation as probability amplitude
came only later and, along with no less a
company than Max Planck, Albert Ein-
stein and de Broglie, he remained skep-
tical about it to the end of his life. Much
later, I was once in a seminar where
someone drew certain quite extended
conclusions from the Schrodinger equa-
tion, and Schrodinger expressed his grave
doubts that it could be taken that seri-
ously; whereupon Gregor Wentzel, who
was also there, said to him: “Schrodinger,
it is most fortunate that other people be-
lieve more in your equation than you
do!”

Schrodinger thought for a time that a
wave packet would represent the actual
shape of an electron, but it naturally
bothered him that the thing had a ten-
dency to spread out in time as if the elec-
tron would gradually get fatter and fat-
ter.

As I said before, I was too green then to
understand these things and still strug-
gled with the older theories. In reading
Debye’s paper of 1923 on the Compton
effect, it occurred to me that, instead of

his assumption of the electron being
originally at rest, one should take into
account its motion on a stationary orbit in
the atom. I thought this was such a good
idea that I even had the incredible cour-
age to go to Debye’s office and tell it to
him. It really wasn’t all that wrong but he
only said: “That’s no way any more to
talk about atoms; you better go and study
Schrodinger ’s new wave mechanics.”

Well, you would not disobey the au-
thorities and, of course, he was again quite
right. So this is what I did; Schrodinger’s
next papers on wave mechanics appeared
shortly, one after the other. I did not
learn about the matrix formulation of
quantum mechanics by Heisenberg, Born
and Pascual Jordan until I read that
paper of Schrodinger’s in which he
showed the two formulations to lead to
the same results. It did not take me too
long to absorb these new methods, and I
wish I could confer to the younger physi-
cists who read this article the marvellous
feeling we students experienced at that
time in the sudden tremendous widening
of our horizon. Since we were not bur-
dened with much previous knowledge, the
process was quite painless for us, and we
were blissfully unaware of the deep
underlying change of fundamental con-
cepts that the more experienced older
physicists had to struggle with.

Although I had already begun an ex-
periment in spectroscopy, I was now en-
tirely captured by theory and I felt the
legal entrance into the guild to be con-
firmed through my acquaintance with
Walter Heitler and Fritz London. They
had just obtained their PhD’s and had
come to Schrodinger’s Institute, where
together they worked on their theory of
covalent bonds. I must have met them in
a seminar, and it was a great thing for me
that they asked me to join them in some
of their walks through the forests around
Zurich. For us students the professors
lived somewhere in the clouds, and that
two real theorists at the ripe age of almost
25 should even bother about a greenhorn
like me was ample cause for my gratitude
to them.

Leipzig

This great period in Zurich came to a
sudden end in the fall of 1927 when some
of the most important men there simul-
taneously succumbed to the pull of the
large magnet in the North, represented by
the flourishing science in Germany. Weyl
had accepted a position in Gottingen,
Schrodinger in Berlin and Debye in
Leipzig, and it was clear to me that 1 had
to join the exodus if I did not want my
time as a student to drag on much longer.
The question was only where to go; I was
tempted to follow either London’s ex-
ample and go with Schrodinger to Berlin,
or Heitler’s, and go to Gottingen.

Before deciding, however, I went to ask
Debye for his opinion, and he advised me
to do neither but instead to come to

PARTICLES AND QUANTA

321

DEBYE

Leipzig. There I would work with
Heisenberg whom he, as the new director
of the Institute of Physics of the Univer-
sity, had persuaded to accept the profes-
sorship for theoretical physics. Debye’s
power of persuasion was quite formidable
and I could not resist it either, particularly
because I had previous evidence of his
sound judgment.

So, in October 1927 before the begin-
ning of the winter semester, I left my nice
home town for the first time, to arrive on
a cold gray morning in that rather ugly
city of Leipzig. The little room I found
for rent from a family overlooked a rail-
road yard; the noise and smoke did not
help much to cheer me up! As soon as I
had completed the simple formality of
registering as a student of the University
in the center of the city I went to the
Physics Institute, which was located near
the outskirts.

It was an old building opposite a cem-
etery on one side and adjoining the garden
of a mental institution on the other, but
occupied by people who were far from
being either dead or crazy. Heisenberg
had not arrived yet and the theorist in
charge was Wentzel who, a year later, was
to become Schrodinger’s successor in
Zurich. I did not find him in his office
and was told by an assistant that I could
see him in his apartment on the third floor
of the building.

It was quite customary at that time for
professors to have official living quarters
in or adjacent to their institutes; Debye
had the Director’s villa in a side wing, and
for young bachelors like Wentzel and also
Heisenberg upon his arrival there were
small but comfortable apartments under
the roof.

I was not at all sure whether it was
really all right to go up there and knock at
his door but I dared to do it anyhow, and
almost from the moment he opened it I
realized that I had come to a new and
much warmer academic climate. Used to
the great distance that separated the
students and professors in freedom-loving
Switzerland, I had expected the prover-
bial discipline of the Germans to call for
an even stricter caste system. Instead,
Wentzel received me with the informal
cordiality of a colleague, which made it
almost difficult for me to address him
with the normal “Herr Professor’’ but
very easy to show him a little paper I had
written before I came to Leipzig.

My paper had been motivated by
Schrodinger’s old dislike of electron
wavepackets’ disagreeable habit of
spreading, and I had had the naive idea
that they might be cured from it at least
partially by radiation damping. To try it
out, I had done a serious calculation for
the harmonic oscillator, with the result
that a suitable gaussian wavepacket,
without spreading, would perform a nice
damped oscillation that led asymptoti-
cally to the wavefunction of the ground
state. Wentzel made some kind com-

ments but modestly disclaimed sufficient
expert knowledge to pass judgment; he
said I should ask Heisenberg, who was
expected in a few days.

My first paper

Although his great achievements dated
back no more than about two years,
Heisenberg was already very famous as
the founder of the new form of mechanics,
which accounted for quantum phenome-
na by abandoning such fundamental ideas
as motion in an orbit and replacing them
by concepts referring to the actual ob-
servation of atomic processes. I think I
lost my breath for a moment when
Wentzel introduced me to this great
physicist in the person of a slender young
man. Maybe Debye had already men-
tioned to him that he knew me from Zur-
ich; in any case, as soon as he shook hands
and started to talk to me in his simple
natural way, I had the feeling that I was
“accepted.”

Just as with Wentzel, there was no in-
dication whatever of a barrier to separate
us on the grounds of Heisenberg’s vastly
superior standing, and this was the ex-
perience I had with many of the other
prominent scientists I later met in Ger-
many. While it surprised me at first, it
had quite a simple reason: These men
were so entirely devoted to their science
and their work spoke so clearly for itself
that there was really no room or reason for
any pretense, be it in the form of grand
manners or of false modesty. With
Heisenberg there was the additional fac-
tor of his youth; as a professor at the age
of 26 he was only about four years older,

although in the time scale of theorists this
already put him something like two gen-
erations ahead of me.

As to my hopes for keeping wavepack-
ets together by radiation damping, he only
smiled and said that, if anything, it could
of course only make them spread even
more. Nevertheless he thought my cal-
culations on the harmonic oscillator were
a good start, and that I should go on to
work them out for the general case. With
the help of P. A. M. Dirac’s paper on ra-
diation effects and a few more tricks, I
managed to do that rather quickly, con-
firming Heisenberg’s prediction, and it
became my first published paper. It ap-
peared in the Physikalische Zeitsch rift as
a precursor to the well known paper of
Victor Weisskopf and Eugene Wigner on
radiation damping and natural line
widths.

Before the Christmas vacations,
Heisenberg said that I should think about
a topic for my doctor’s thesis: This I did
mostly while skiing in Switzerland after
I had gone home. I knew the importance
of Paul Ehrenfest’s adiabatic theorem in
the older quantum theory, and when I
went back to Leipzig after New Year I
proposed for my thesis its reformulation
in quantum mechanics.

“Yes,” said Heisenberg, “one might do
that, but I think you had better leave such
things to the learned gentlemen of Got-
tingen.”

What he meant was the school of Born,
which had the reputation of being par-
ticularly skilled in, and rather fond of,
elaborate mathematical formalisms.
Instead, he suggested something more

322

HISTORY OF PHYSICS

in a metal so as to avoid a mean free path
of the order of atomic distances. Such a
distance was much too short to explain
the observed resistances, which even de-
manded that the mean free path become
longer and longer with decreasing tem-
perature. But Heitler and London had
already shown- how electrons could jump
between two atoms in a molecule to form
a covalent bond, and the main difference
between a molecule and a crystal was only
that there were many more atoms in a
periodic arrangement. To make my life
easy, I began by considering wavefunc-
tions in a one-dimensional periodic po-
tential. By straight Fourier analysis I
found to my delight that the wave differed
from the plane wave of free electrons only
by a periodic modulation.

This was so simple that I didn’t think
it could be much of a discovery, but when
I showed it to Heisenberg he said right
away: “That’s it!” Well, that wasn’t
quite it yet, and my calculations were only
completed in the summer when I wrote
my thesis on “The Quantum Mechanics
of Electrons in Crystal Lattices.”

I then left Leipzig to become for a year
the assistant of Pauli in Zurich and to
spend another year as Lorentz Fellow in
Holland. It was not until the fall of 1930
that I returned to Leipzig, this time as
Heisenberg’s assistant, and by then the
early days of quantum mechanics were
really over, although many of its impor-
tant consequences were yet to come — and
are still coming.

I don’t think many of us realized that
we had just gone through quite a unique
era; we thought that this was just the way
physics was normally to be done and only

wondered why clever people had not seen
that earlier. Almost any problem that
had been tossed around years before could
now be reopened and made amenable to
a consistent treatment. To be sure, there
were a few minor difficulties left, such as
the infinite self -energy of the electron and
the question of how it could exist in the
nucleus before beta decay; and nobody
had yet derived the numerical value of the
fine-structure constant. But we were
sure that the solutions were just around
the corner and that any new ideas that
might be called for in the process would be
easily supplied in the unlikely event that
this should be necessary. Well, the last
fifty years have taught us at least to be a
little more modest in our expectations.

Heisenberg the teacher and scientist

From what I have told about the year
when I had the good fortune to be
Heisenberg’s first student it may already
be evident that he stands in the center of
my memories of this most formative pe-
riod in my life as a physicist. It is not only
that he suggested the theme of my thesis,
but I owe it to him that I caught the real
spirit of research and that I dared to take
the first steps in learning how to walk. If
I should single out one of his great quali-
ties as a teacher, it would be his im-
mensely positive attitude towards any
progress and the encouragement he
thereby conferred.

This does not mean that one always
received praise from him and that, on
occasions, he could not be quite severe.
Once during my thesis work I became
stuck on a rather awkward difficulty and
hoped that he would help me out. But

WENTZEL

SCHRODINGER

down to earth such as, for example, fer-
romagnetism or the conductivity of met-
als.

As to ferromagnetism, he thought that
it had to be explained by an exchange in-
tegral between electrons, with the oppo-
site sign from that in helium so as to favor
a parallel rather than opposite orientation
of their spins. He had shown before that
the difference between the ortho and para
states of the helium atom were due to the
dependence of the exchange energy on
their symmetry properties and had also
recognized that the analogous phenome-
non for the protons in the hydrogen mol-
ecule led to the two forms, ortho and para,
of hydrogen. Well, his idea sounded so
convincing that I felt there was no point
of my going into it. It was obvious to me
that Heisenberg already knew the essen-
tials; indeed, .he soon wrote the paper on
the subject that laid the groundwork for
the modern theory of ferromagnetism. It
was not until two years later that I some-
what embellished his treatment by the
introduction of spinwaves.

Electrons in crystals

There was a greater challenge in his
other suggestion, to do something more
about the properties of metals. Going
beyond the earlier work of Paul Drude
and H. A. Lorentz, Wolfgang Pauli had
already given a first new impetus to the
field by invoking Fermi statistics to ex-
plain the temperature-independent par-
amagnetism of conduction electrons;
Sommerfeld had gone further by dis-
cussing the consequences for the specific
heat and the relation between the thermal
and the electric conductivity of metals.
Both, however, had treated the conduc-
tion electrons as an ideal gas of free elec-
trons, which didn’t appear in the least
plausible to me.

When I started to think about it, I felt
that the main problem was to explain how
the electrons could sneak by all the ions

l

A

PARTICLES AND QUANTA

323

PAULI

after I had explained it to him he only
said: “Now that you have analyzed the
source of the trouble it can’t be all that
hard to see what to do about it.”

Of course, I felt rather depressed, but
just to get out of it I pushed once more
and in some cumbersome way finally
managed indeed to get over the obstacle.
It was not the mathematical method but
only physical content that ever mattered
to Heisenberg. As to elegance he might
have agreed with Ludwig Boltzmann’s
opinion that it was “best left to tailors and
bootmakers.”

Besides my year as Heisenberg’s stu-
dent, I spent the two more years, 1930-31
and 1932-33, in Leipzig until Hitler suc-
ceeded in forming a new Germany in his
own frightful image. What followed is
too well known for me to dwell upon, but
I cannot refrain from one sad comment on
human nature. The very devotion to

their work and their detachment from the
dark irrational passions spreading around
them caught most of even the finest Ger-
man scientists unprepared for the on-
coming flood. Those who did not leave
were with few exceptions swept along and
were left, each in his own way, to struggle
with their inner conflicts.

But my memories of Heisenberg belong
to the happier time before those events.
Many of them relate to entirely informal
and anything-but-professional conver-
sations on walks, in his ski hut in the Ba-
varian Alps or under other relaxed cir-
cumstances. These remain no less pre-
cious to me than our talks on physics, and
I want to tell in conclusion about two of
them that I remember most vividly.

Once I came back after dinner to my
room in the Institute to finish some work.
While I sat at my desk I heard Heisen-
berg, who was an excellent pianist, playing
in his apartment under the roof of the
building. It was already late at night
when he came down to my room and said
he just wanted to talk a little before going
to bed after he had practiced a few bars of
a Schumann concerto for three hours.
And then he told me that Franz Liszt,
when he was already a famous pianist,
found that his scales of thirds and fifths
were not smooth enough. So he cancelled
all engagements, and for a year practiced
nothing but these scales before he started
to perform again. The reason I remem-
ber this so well is that I felt that Heisen-
berg, without intention, had told me
something important about himself. The
audience of Liszt after that year must
have thought it a wonder how easily he
was able to play those difficult scales.
But the real wonder was of course that he
had had the strength and the gift of con-
centration to keep on perfecting them
incessantly for a whole year.

Now, one of the most marvellous traits
of Heisenberg was the almost infallible
intuition that he showed in his approach

to a problem of physics and the pheno-
mental way in which the solutions came
to him as if out of the blue sky. I have
asked myself whether that wasn’t a form
of the “Liszt phenomenon,” and for that
the more admirable. Not that Heisen-
berg would ever have cancelled all other
activity for a year to master a special
technique. But we all knew the dreamy
expression on his face, even in his com-
plete attention to other matters and in his
fullest enjoyment of jokes or play, which
indicated that in the inner recesses of the
brain he continued his all-important
thoughts on physics.

There is another remark he once made
that I consider even more characteristic.
We were on a walk and somehow began to
talk about space. I had just read Weyl’s
book Space, Time and Matter, and under
its influence was proud to declare that
space was simply the field of linear oper-
ations.

“Nonsense,” said Heisenberg, “space is
blue and birds fly through it.”

This may sound naive, but I knew him
well enough by that time to fully under-
stand the rebuke. What he meant was
that it was dangerous for a physicist to
describe Nature in terms of idealized ab-
stractions too far removed from the evi-
dence of actual observation. In fact, it
was just by avoiding this danger in the
previous description of atomic phenom-
ena that he was able to arrive at his great
creation of quantum mechanics. In cel-
ebrating the fiftieth anniversary of this
achievement, we are vastly indebted to
the men who brought it about: not only
for having provided us with a most pow-
erful tool but also, and even more signif-
icant, for a deeper insight into our con-
ception of reality.

* * *

This article is an adaptation of a talk given 26
April 1976 at the Washington, DC meeting of
The American Physical Society.

324

HISTORY OF PHYSICS

Electron diffraction:
fifty years ago

A look back at the experiment that established the wave nature
of the electron, at the events that led up to the discovery, and at the
principal investigators, Clinton Davisson and Lester Germer.

Richard K. Gehrenbeck

An article that appeared in the December
1927 issue of Physical Review, “Diffrac-
tion of Electrons by a Crystal of Nickel,”
has been referred to in countless articles,
monographs and textbooks as having es-
tablished the wave nature of the elec-
tron— in principle, of all matter.1 Now,
fifty years later, it is fitting to look back at
the events that led up to this historical
discovery and at the discoverers, Clinton
Davisson and Lester Germer. Figure 1
shows them in their lab in 1927, together
with their assistant Chester Calbick.

A shy midwesterner

Clinton Joseph Davisson, the senior in-
vestigator, was born in Bloomington, Il-
linois, on 22 October 1881, the first of two
children. His father, Joseph, who had
settled in Bloomington after serving in the
Civil War, was a contract painter and
paperhanger by trade. His mother,
Mary, occasionally taught in the Bloom-
ington school system. Their home was,
as Davisson’s sister, Carrie, characterized
it, “a happy congenial one — plenty of love
but short on money.”

Davisson, slight of frame and frail
throughout his life, graduated from high
school at age 20. For his proficiency in
mathematics and physics he received a
one-year scholarship to the University of
Chicago; his six-year career there was in-
terrupted several times for lack of funds.
He acquired his love and respect for
physics from Robert Millikan; Davisson
was “delighted to find that physics was
the concise, orderly science [he] had im-
agined it to be, and that a physicist [Mil-
likan] could be so openly and earnestly
concerned about such matters as colliding
bodies.”

Richard K. Gehrenbeck is an assoicate pro-
fessor of physics and astronomy at Rhode
Island College, Providence, Rhode Island.

Before finishing his undergraduate
degree at Chicago, he became a part-time
instructor in physics at Princeton Uni-
versity, where he came under the influ-
ence of the British physicist Owen Rich-
ardson, who was directing electronic re-
search there. Davisson’s PhD thesis at
Princeton, in 1911, extended Richardson’s
research on the positive ions emitted from
salts of alkaline metals. Davisson later
credited his own success to having caught
“the physicist’s point of view — his habit
of mind — his way of looking at things”
from such men as Millikan and Richard-
son.

After completing his degree, Davisson
married Richardson’s sister, Charlotte,
who had come from England to visit her
brother. After a honeymoon in Maine
Davisson joined the Carnegie Institute of
Technology in Pittsburgh as an instructor
in physics. The 18-hour-per-week
teaching load left little time for research,
and in six years there he published only
three short theoretical notes. One nota-
ble break during this period was the
summer of 1913, when Davisson worked
with J. J. Thomson at the Cavendish
laboratory in England.

In 1917, after he was refused enlistment
in the military service because of his
frailty, Davisson obtained a leave of ab-
sence from Carnegie Tech to do war-re-
lated research at the Western Electric
Company, the manufacturing arm of the
American Telephone and Telegraph
Company, in New York City. His work
was to develop and test oxide-coated
nickel filaments to serve as substitutes for
the oxide-coated platinum filaments then
in use. At the end of World War I he
turned down an offered promotion at
Carnegie Tech to accept a permanent
position at Western Electric. It was at
this time that he began the sequence of
investigations that ultimately led to the

PHYSICS TODAY / JANUARY 1978

discovery of electron diffraction; it was
also at this time that he was joined by a
young colleague, Lester Halbert Germer,
just discharged from active service.

An adventurous New Yorker

Germer was born on 10 October 1896,
the first of two children of Hermann
Gustav and Marcia Halbert Germer, in
Chicago, where Dr Germer was practicing
medicine. In 1898 the family moved to
Canastota in upper New York state, the
childhood home of Mrs Germer. Ger-
mer’s father became a prominent citizen
in the little town on the Erie canal, serving
as mayor, president of the board of edu-
cation and elder in the Presbyterian
church.

Germer attended school in Canastota
and won a four-year scholarship to Cor-
nell University, graduating from there in
the spring of 1917, six weeks early because
of the outbreak of the war. The local
newspaper, after applauding 18-year-old
Lester for working as a laborer for the
local paving contractors during his sum-
mer vacation, proceeded to ridicule his
lazier contemporaries for sitting “day
after day in the lounging places of the
village,” saying there is “nothin’ doin’ ”
and that “a young feller has no chanst in
this durn town.” (Lester, must have
taken a bit of ribbing from the “idle boys”
after this appeared!) Germer’s studies at
Cornell were partly self-directed; in their
junior year he and two classmates, finding
themselves “unsatisfied with the course
in electricity and magnetism given . . .
bought a more advanced text and met
regularly in the vacant class room . . . and
really learned something.”

Upon graduation from Cornell, Germer
obtained a research position at Western
Electric, which he held for about two
months before volunteering for the Army
(aviation section of the signal corps). He

PARTICLES AND QUANTA

325

apparently made no contact with Davis-
son then. Lieutenant Germer, among
those piloting the first group of airplanes
on the Western Front, was officially
credited with having brought down four
German warplanes. Discharged on 5
February 1919, Germer was treated in
New York City for severe headache, ner-
vousness, restlessness and loss of sleep,
conditions attributed to his military
campaigns, but he refused to file for
compensation because “others were worse
off.” After three weeks of rest, he was
re-hired by Western Electric — and had as
his first assignment the preparation of an
annotated bibliography for a new project
being directed by his new supervisor,
Davisson.

That fall Germer married his Cornell
sweetheart, Ruth Woodard of Glens Falls,
New York.

Electron emission — in court

The assignment that engaged Davisson
and Germer in their first joint effort re-
flects one of the chief interests of the
parent company, AT&T, at this time: to
conduct a fundamental investigation into
the role of positive-ion bombardment in
electron emission from oxide-coated
cathodes. Although Germer later re-
membered this project as having been
directly related to the famous Arnold-
Langmuir patent suit, that occupied
Western Electric (Harold Arnold) and
General Electric (Irving Langmuir) from
1916 until it was finally settled2 by the US
Supreme Court (in favor of Western
Electric) in 1931, a careful examination of
the documents makes it clear that Dav-
isson and Germer’s project could have
related to it only in a very indirect way.
The patent case concerned improvements
to the earliest deForest triode tubes with
metallic (tungsten or tantalum) cathodes;
it dealt with evidence obtained in the

years 1913 to 1916, before Davisson and
Germer appeared on the scene. Never-
theless, because AT&T was deeply con-
cerned about the efficiency and effec-
tiveness of its triode amplifiers — key
components in its recently constructed
transcontinental telephone lines — Arnold
assigned Davisson and Germer the task of
conducting tests on oxide-coated cath-
odes. They published their results in the

Physical Review in 1920, concluding that
positive-ion bombardment has a negligi-
ble effect on the electron emission from
oxide-coated cathodes.3

With this problem settled, a related
question came up: What is the nature of
secondary electron emission from grids
and plates subjected to electron bom-
bardment? Davisson was assigned this
new task and given an assistant, Charles

BELL LABORATORIES

Davisson, Germer and Calbick in 1927, the year they demonstrated electron diffraction. In their
New York City laboratory are Clinton Davisson, age 46; Lester Germer, age 31, and their assistant
Chester Calbick, age 23. Germer, seated at the observer’s desk, appears ready to read and record
electron current from the galvanometer (seen beside his head); the banks of dry cells behind Davisson
supplied the current for the experiments. Figure 1

NUMBER OF ELECTRONS

326

HISTORY OF PHYSICS

Electron-scattering peak. The energy of the scattered electrons varies from almost zero to that
of the incident beam (indicated by the arrow). This is a reconstruction of the type of observation
that led Davisson and Charles Kunsman to conclude that some electrons were being scattered
elastically. Davisson saw these as possible probes of the electronic structure of the atom, in analogy
to Rutherford's use of alpha particles to explore the nucleus. Figure 2

H. Kunsman, a new PhD from the Uni-
versity of California. F or this work they
were able to convert the positive-ion ap-
paratus to an electron-beam apparatus.
Meanwhile Germer was shifted to a
project on the measurement of the
thermionic properties of tungsten, a topic
he pursued for about four years, both
under Davisson’s direction and as part of
a graduate program he undertook at
nearby Columbia University part time.

A startlihg observation

Soon after Davisson and Kunsman
began their secondary electron emission
studies, they observed an unexpected
phenomenon that was to have crucial
importance for their future experimental
program: A small percentage (about 1%)
of the incident electron beam was being
scattered back toward the electron gun
with virtually no loss of energy — the
electrons were being scattered elastically.
Figure 2 reconstructs this phenomenon.
Previous observers had noticed this effect
for low-energy electrons (about 10 eV),
but none had reported it for electrons of
energies over 100 eV.

Although this discovery undoubtedly
had no immediate impact on the stock-
holders of AT&T, it affected Davisson
profoundly. To him these elastically
scattered electrons appeared as ideal
probes with which to examine the ex-
tranuclear structure of the atom. Ernest
Rutherford announced his nuclear model
of the atom in 1911, the year Davisson
completed his PhD; Hans Geiger and
Ernest Marsden completed their defini-
tive experimental tests of Rutherford’s
theory and Niels Bohr announced his
planetary model of the atom in 1913,
when Davisson worked with Thomson at
Cambridge. So it is not surprising that
Davisson was enthusiastic about the
prospect of using these electrons for basic
research on the structure of the atom. In

Davisson’s own words,

“The mechanism of scattering, as we
pictured it, was similar to that of
alpha ray scattering. There was a
certain probability that an incident
electron would be caught in the field
of the atom, turned through a large
angle, and sent on its way without loss
of energy. If this were the nature of
electron scattering it would be possi-
ble, we thought, to deduce from a sta-
tistical study of the deflections some
information in regard to the field of
the deflecting atom . . . What we were
attempting . . . were atomic explora-
tions similar to those of Sir Ernest
Rutherford ... in which the probe
should be an electron instead of an
alpha particle.”

In fact, Davisson was so enthusiastic
about a full-scale assault on the atom that
he was able to convince his superiors to let
him and Kunsman devote a large fraction
of their time to it, and to give them the
necessary shop backup.

The basic piece of apparatus, built to
order by a talented machinist and glass-
blower, Geroge Reitter, was a vacuum
tube with an electron gun, a nickel target
inclined at an angle of 45° to the incident
electron beam and a Faraday-box collec-
tor, which could move through the entire
135° range of possible scattered electron
paths; it is diagrammed in figure 3. The
Faraday box was set at a voltage to accept
electrons that were within 10% of the in-
cident electron energy.

After two months of experimentation,
Davisson and Kunsman submitted a
two-column paper to Science, in which
they sketched the main features of their
scattering program, presented a typical
curve of their data, proposed a shell model
of the atom for interpreting these results,
and offered a formula for the quantitative
prediction of the implications of the
model.4 Unfortunately their attempts to

link together their data, the model and
the predictions were anything but defi-
nite— quite out of keeping with the
Rutherford-Geiger-Marsden tradition.

Although Davisson (and Kunsman)
must have been somewhat disappointed
at the limited success of their initial ven-
ture, they pressed on with additional ex-
periments. In the next two years they
built several new tubes, tried five other
metals (in addition to nickel) as targets,
developed rather sophisticated experi-
mental techniques at high vacuum (“the
pressure became less than could be mea-
sured, i.e., less than 10~8 mm Hg,”) and
made valiant theoretical attempts to ac-
count for the observed scattering inten-
sities. The results were uniformly un-
impressive; several of the studies were not
even published. In fact, the generally
disheartened atmosphere that seems to
have prevailed by the end of 1923 is indi-
cated by the fact that Kunsman left the
company and Davisson abandoned the
scattering project.

A year later, however, Davisson was
ready to have another try at electron
scattering. Was this change of heart
prompted by Davisson’s strong attraction
to the project? Was it his eagerness to
obtain additional information about the
extranuclear structure of the atom? In
any case, in October 1924 Germer was put
back on the scattering project in place of
the departed Kunsman. Germer, who
had already completed several therm-
ionic-emission studies, was returning to
Western Electric after a 15-month illness.
Regarding his development as a physicist
by this time, Germer later recollected:

“I learned relatively little at Columbia
. . . but was nevertheless fortunate in
working . . . with Dr C. J. Davisson. I
learned a simply enormous amount
from him. This included how to do
experiments, how to think about
them, how to write them up, how even
to learn what other people had pre-
viously done in the field ... I am quite
certain that I do really owe to Dr Dav-
isson much the best part of my educa-
tion, and I am not really convinced
that it is so inferior to that obtained in
more conventional ways. It is cer-
tainly different.”

A “lucky break” and a new model

So the scattering experiments were fi-
nally resumed. One can easily imagine,
then, the feelings of disappointment and
frustration that Davisson and Germer
must have shared when, soon after the
project had been restarted, they discov-
ered a cracked trap and badly oxidized
target on the afternoon of 5 February
1925, as the notebook entry in figure 4
shows. What it meant in simple terms
was that the experiments with the spe-
cially polished nickel target, discontinued
for almost a year, were to be delayed
again. Apparently Germer’s attempts to
revitalize the tube after its long period of

PARTICLES AND QUANTA

327

Electron gun

Scheme of the first scattering tube, which served as a prototype for the group's later models.
Davisson and Germer later included mechanisms for rotating the target azimuthally 360° about
the beam axis and for changing the angle of the incident beam with respect to the normal to the
target. In their 1926-27 work the incident beam was perpendicular to the target face, and the
scattering angle was called the ' ‘colatitude angle.” Figure 3

disuse by repumping and baking (out-
gassing) were to be for nought; an addi-
tional delay for repairs was necessary.

This was not the only time that a tube
had broken during a scattering experi-
ment, nor was it to be the last. Nor was
the method of repair unique, for the
method of reducing the oxide on the
nickel target by prolonged heating in
vacuum and hydrogen had been used once
before (unsuccessfully; that time it had
led to the formation of a “black precipi-
tate” and “no apparent cleaning up of the
nickel”). This particular break and the
subsequent method of repair, however,
had a crucial role to play in the later dis-
covery of electron diffraction.

By 6 April 1925 the repairs had been
completed and the tube put back into
operation. During the following weeks,
as the tube was run through the usual se-
ries of tests, results very similar to those
obtained four years earlier were obtained.
Then suddenly, in the middle of May,
unprecedented results began to appear, as
shown in figure 5. These so puzzled
Davisson and Germer that they halted the
experiments a few days later, cut open the
tube, and examined the target (with the
assistance of the microscopist F. F. Lucas)
to see if they could detect the cause of the
new observations.

What they found was this: The poly-
crystalline form of the nickel target had
been changed by the extreme heating
until it had formed about ten crystal fac-
ets in the area from which the incident
electron beam was scattered. Davisson
and Germer surmised that the new scat-
tering pattern must have been caused by
the new crystal arrangement of the target.
In other words, they concluded that it was
the arrangement of the atoms in the
crystals, not the structure of the atoms,
that was responsible for the new intensity
pattern of the scattered electrons.

Thinking that the new scattering pat-
terns were too complicated to yield any
useful information about crystal struc-
ture, Davisson and Germer decided that
a large single crystal oriented in a known
direction would make a more suitable
target than a collection of some ten small
facets randomly arranged. Because nei-
ther Davisson nor Germer knew much
about crystals, they, assisted by Richard
Bozorth, spent several months examining
the damaged target and various other
nickel surfaces until they were thoroughly
familiar with the x-ray diffraction pat-
terns (note!) obtained from nickel crystals
in various states of preparation and ori-
entation.

By April 1926 they had obtained a
suitable single crystal from the company’s
metallurgist, Howard Reeve, and cut,
etched and mounted it in a new tube that
allowed for an additional degree of free-
dom of measurement ; the collector could
now rotate in azimuth (the 360° angle
circling the beam axis) as well as in cola-
titude. The design of the new tube re-

flected their expectation of finding certain
“transparent directions” in the crystal
along which the electrons would move
with least resistance. They expected
these special directions to coincide with
the unoccupied lattice directions.

More than a “second honeymoon”

Having suffered disappointment with
the results of the original scattering ex-
periments performed with Kunsman,
Davisson must have been doubly
disheartened by the meager returns he
and Germer obtained with the new tube.
After an entire year spent in preparation,
and with a new tube and a new theory in
hand, they obtained experimental results
that were even less interesting than those
from the earliest experiments. The new
colatitude curves showed essentially
nothing, and even the new azimuth curves
gave at best only a weak indication of the
expected three-fold symmetry of the
nickel crystal about the incident beam.

Davisson must have been quite pleased
with the prospect of getting away for a few
months during the summer of 1926, when
he and his wife had planned a vacation
trip to relax and visit relatives in England.
Mrs Davisson recalled that this summer
had been chosen for the trip because her
sister, May, and brother-in-law, Oswald
Veblen of Princeton University, were
available to stay with the Davisson chil-
dren at that time. As Davisson wrote to
his wife, then at the Maine cottage mak-

ing arrangements for the children: “It
seems impossible that we will be in Oxford
a month from today — doesn’t it? We
should have a lovely time — Lottie dar-
ling— It will be a second honeymoon —
and should be sweeter even than the
first.” Something was to happen on this
particular trip, however, to turn it into
more than the “second honeymoon”
Davisson envisioned.

Theoretical physics was undergoing
fundamental changes at this time. In the
early months of 1926 Erwin Schrodinger’s
remarkable series of papers on wave me-
chanics appeared, following Louis de
Broglie’s papers of 1923-24 and Albert
Einstein’s quantum-gas paper of 1925.
These papers, along with the new matrix
mechanics of Werner Heisenberg, Max
Born and Pascual Jordan, were the
subject of lively discussions at the Oxford
meeting of the British Association for the
Advancement of Science. Davisson, who
generally kept abreast of recent develop-
ments in his field but appears to have
been largely unaware of these recent de-
velopments in quantum mechanics, at-
tended this meeting. Imagine his sur-
prise, then, when he heard a lecture by
Born in which his own and Kunsman’s
(platinum-target) curves of 1923 were
cited as confirmatory evidence for de
Broglie’s electron waves!5

After the meeting Davisson met with
some of the participants, including Born
and possibly P.M.S. Blackett, James

328

HISTORY OF PHYSICS

The notebook entry for 5 February 1925 records, in Germer's handwriting, the discovery of the
broken tube that interrupted the scattering experiments once again. It was this break, however,
which initiated a chain of events that eventually led to the preparation of a single crystal of nickel
as the target, and to a shift of Davisson's interest from atomic structure to crystal structure. Re-
produced by courtesy of Bell Laboratories. Figure 4

Franck and Douglas Hartree, and showed
them some of the recent results that he
and Germer had obtained with the single
crystal. There was, according to Davis-
son, "much discussion of them.” All this
attention might seem strange in light of
the relatively feeble peaks Davisson and
Germer had obtained, but even these may
have been exciting to physicists already
convinced of the basic correctness of the
new quantum theory. It may also reflect
the fact that several European physicists,
Walter Elsasser (Gottingen), E.G. Dy-
mond (Cambridge, formerly Gottingen
and Princeton), and Blackett, James
Chadwick and Charles Ellis of Cam-
bridge6 had attempted similar experi-
ments and abandoned them because of
the difficulties of producing the required
high vacuum and detecting the low-in-
tensity electron beams. Apparently they
were encouraged by these results, which
appeared so unimpressive to Davisson.
At any rate, Davisson spent "the whole of
the westward transatlantic voyage . . .
trying to understand Schrodinger’s pa-
pers, as he then had an inkling . . . that the
explanation might reside in them” — no
doubt to the detriment of the “second
honeymoon” in progress.

Back at Bell Labs (as the engineering
arm of Western Electric has been called
since 1925), Davisson and Germer exam-
ined several new curves that Germer had
obtained during Davisson’s absence.
They found a discrepancy of several de-
grees between the observed electron in-
tensity peaks and the angles they ex-
pected from the de Broglie-Schrodinger
theory. To pursue this matter further
they cut the tube open and carefully ex-
amined the target and its mounting.
After finding that most of the discrepancy
could be accounted for by an accidental
displacement of the collector-box open-
ing, they “laid out a program of thorough
search” to pursue the quest of diffracted
electron beams. In typical Davisson

fashion, however, this quest was preceded
by a period of careful preparation, in-
cluding an important change in the ex-
perimental tube. As Davisson wrote to
Richardson in November,

"I am still working at Schrbdinger and
others and believe that I am beginning
to get some idea of what it is all about.
In particular 1 think that I know the
sort of experiment we should make
with our scattering apparatus to test
the theory.”

Found — a “quantum bump”

It was three weeks before the “thorough
search" was begun. The importance that
Davisson (and Bell Labs) had come to
attach to this project can be surmised
from the addition to it of a new assistant,
Chester Calbick, a recently graduated
electrical engineer. After about a month
of experimenting, during which time
Calbick took charge of operating the ex-
periment, they gave the newly prepared
tube a thorough set of consistency tests.
During one attempt by Germer to reacti-
vate the tube in late November the tube
broke, but with little damage. (Strangely,
little damage can be considered “lucky”
in this case, whereas it would have been
“unlucky” in the case of the 1925
break!)

The first experiments with the new
tube yielded no significant results; the
colatitude and azimuth curves looked
much as before, and the new experiments
added by Davisson “to test the theory”
were uninformative as well. These tests
consisted of varying the accelerating
voltage, and hence electron energy E, for
fixed colatitude and azimuth settings, and
were designed to see if any effect could be
discerned for a changed electron wave-
length X, according to the de Broglie re-
lationship, X = h/( 2 mE)1/2.

A concerted search for “quantum
peaks” (voltage-dependent scattered
electron beams) was launched by late

December. These attempts revealed only
“very feeble” peaks. The situation
changed dramatically on 6 January 1927,
however; the data for that day are ac-
companied by the remark, in Calbick’s
neat handwriting: “Attempt to show
‘quantum hump’ at an intermediate [co-
latitude] angle. Bump develops at 65 V,
compared with calculated value for
‘quantum bump’ of V = 78 V." Then,
stretched across the bottom of the page in
Germer’s unmistakable bold strokes, is
the additional remark: "First Appear-
ance of Electron Beam." A portion of the
notebook page is reproduced in figure 6.

The data for this curve are extremely
interesting. Noting from the figure that
the readings were taken in one-volt in-
tervals on either side of 79 volts, whereas
the steps are 2, 5 and then 10 volts else-
where, we see that a peak was expected at
about 78 volts. But the experiment
yielded a single large current at 65 volts.
The experimenters took immediate notice
of this spike, making a second run in
one-volt steps around 65 volts, which on
a graph shows a clear peak centered on 65
volts. It is easy to imagine the excitement
that must have accompanied this sudden
turn of events, moving Germer to sprawl
his glad tidings across the bottom of the
page!

With this single critical result in hand,
the experimental situation changed sud-
denly. The next day, 7 January, they ran
several additional voltage curves, one for
each of four different colatitude positions.
A voltage peak appeared at a colatitude
angle of 45° that was even greater than
that at 40°, where the collector had been
set the previous day. On the eighth, a
new colatitude curve was run at a voltage
of 65 volts, and the first true and unmis-
takable colatitude peak was observed —
this was what Davisson had been looking
for since 1920! Skipping Sunday, they
next ran an azimuth curve at 65 volts and
a colatitude of 45°. ’This time the three-
fold azimuthal symmetry was immedi-
ately apparent. Figure 7 shows these
curves.

The experiments that were carried out
during the next two months show that
Davisson, Germer and Calbick, having
finally found and positively identified one
set of electron beams, could now find and
identify others quickly. This block of
experiments continued through 3 March,
when Calbick left for a month on family
business. Comparing this with earlier
periods of Davisson’s long contact with
electron scattering, we see that not since
the early days of the original Davisson-
Kunsman experiments had there been
such intense and concentrated effort in a
single well defined direction. The pres-
ence of a clear, unambiguous goal cer-
tainly must have been a major factor in
the two cases, an ingredient lacking at
other times.

Another factor undoubtedly urging
Davisson on to rapid (but careful) exper-

PARTICLES AND QUANTA

329

imentation and possible early publication
was his feeling that others might be
pursuing similar investigations at that
time. Recalling his conversations at
Oxford and the comments that had been
made about the interest of others in this
matter, he sent off an article to Richard-
son in March with the accompanying
note:

“I hope you will be willing, if you
think it at all desirable, to get in touch
with the editor of Nature with the
idea of securing early publication.
We know of three other attempts that
have been made to do this same job,
and naturally we are somewhat fearful
that someone may cut in ahead of us.”
As it turned out these efforts had long
been abandoned, but he had no way of
knowing that. Nevertheless, another
investigator, unknown to Davisson at that
time, was indeed making progress at re-
vealing the phenomena of electron dif-
fraction with high-voltage electrons and
thin metal foils. This was J.J.’s son, G.P.
Thomson; his and Andrew Reid’s first
note was published in Nature just one
month after Davisson and Germer’s.7

A conservative note and a bold one

Davisson and Germer’s Nature article
was an extremely conservative expression
of the new experimental evidence for
electron diffraction.8 Its title, “The
Scattering of Electrons by a Single Crystal
of Nickel,” bears a closer connection to
the early work of Davisson and Kunsman
than it does to the new wave mechanics.
Although the paper included a table
linking the scattered electron peaks to the
corresponding de Broglie wavelengths, it
was not until the last two paragraphs that
a tentative suggestion was made about the
important implications of the work: The
results were “highly suggestive ... of the
ideas underlying the theory of wave me-
chanics.”

This cautious attitude may have been
due to the problem that Davisson and
Germer had in making the proper corre-
lation between their data points and the
theory; they found it necessary to hy-
pothesize an ad hoc “contraction factor”
of about 0.7 for the nickel-crystal spacing
to get approximate correspondence be-
tween the de Broglie wavelengths and
their data. Even at that, only eight of the
thirteen beams described were clearly
amenable to this analysis.

This cautious attitude appears to have
been abandoned in a concurrent article by
Davisson alone for an in-house publica-
tion, the Bell Labs Record.9 The very
title, “Are Electrons Waves?” suggests
this difference. After reviewing the evi-
dence that led Max von Laue to think of
x rays as being wave-like, he cited his and
Germer’s recent work with electrons,
urging a similar conclusion in this case.
Although this article gave its readers no
actual data on the experimental evidence
for electron waves, it clearly indicates that

Before and after the accident of 5 February
1925. Although the first scattering curves after
the repair of the broken tube (middle curve) re-
sembled the 1921 results of Davisson and
Kunsman (top curve), striking peaks soon made
a sudden appearance (bottom). This develop-
ment led Davisson and Germer to make a major
change in their program. Figure 5

Davisson’s thoughts (and certainly Ger-
mer’s as well) on the subject were not
nearly as reserved as the Nature article
suggests.

One other public announcement of the
recent discoveries was made at this time.
In a paper presented at the Washington
meeting of The American Physical Soci-
ety on 22-23 April 1927 and abstracted in
the Physical Review in June,10 Davisson
and Germer basically repeated what they
had stated in their Nature article, and
then added an intriguing final paragraph.
Referring to the three anomalous beams
that could not be fitted into the analysis
in the Nature article, they suggested that
these “offer strong evidence that there
exists in this crystal a structure which has
not been hitherto observed for nickel.”
This statement implies Davisson and
Germer had already gone beyond the
point of using the “known” structure of
the nickel crystal to find out about the
possibility of the wave properties of the
electron; they were now using the
“known” electron waves to learn new facts
about the nickel crystal. Between March,
when the Nature article was submitted,
and April, when the Phys. Rev. abstract
was prepared, results that had been em-
barrassing to the theory had become a
potential new application of that very
theory!

True to form, however, Davisson and
Germer did not sit back and rest on a “job
well done”; they recognized the consid-
erable work necessary to resolve a number
of questions still outstanding. Among
these were:

► the problem of the “anomalous” beams
mentioned above,

► the ad hoc “contraction factor” that
they had found necessary to attribute to
the nickel crystal and

► extension of their electron energies
over a greater range, and sharpening and
refining their diffraction peaks.

Instant acclaim

Toward this end they initiated an ex-
tensive experimental and theoretical at-
tack that lasted from 6 April (when Cal-
bick returned from his month’s absence)
until 4 August. At that time the tube was
cut open for a final careful examination of
the target and the other tube components.
As it turned out, this intention was foiled
when, in the process of being brought
back to room temperature, the tube “blew
up and [was] partially ruined . . . the leads
being broken, filament also, and a large
part of the nickel oxidized.” A broken
tube had served to initiate the decisive
experiments on 5 February 1925, and a
broken tube ended them on 4 August
1927, two and a half years later.

The most interesting of this last group
of experiments was a series designed to
investigate “the anomalous peaks after
bombardment,” which appeared for a
restricted period of time after the target
had been heated by bombardment. The
experiments showed that the nature —
even the existence — of certain beams was
not static but varied with temperature
and time (and hence conditions of the
target in terms of occluded gases). The
notebook entries include a great variety
of different terms, diagrams and calcula-
tions designed to try to make sense out of
these data. Davisson and Germer found
a “gas crystal” model, in which “gas atoms
fit into the crystal,” to be the most effec-
tive.

The task of welding data and interpre-
tation into a comprehensive report for
publication was begun in mid June, well
before the experiments were completed.
It appears that Davisson was responsible
for most, if not all, of the writing; in a let-
ter to his family at the summer cottage he
wrote:

“I’m busy these days writing up our
experiment — It’s an awful job for me.
I didn’t get much done yesterday as
Prof. Epstein from Pasadena turned
up and had to be entertained and
shown things — and today I’m too slee-
py [after having spent last evening at
the theater with Karl Darrow], How-
ever, I must keep at it.”

More than three weeks later (23 July) he

330

HISTORY OF PHYSICS

The sixth of January 1927 might well be regarded as the birthday of electron waves, for it was the
day that data directly supporting the de Broglie hypothesis of electron waves were first observed.
Note the peak deflection at 65 volts, and the detailed study of the region directly below. Calbick's
handwriting is neat and cautious; Germer’s is bold and expansive. Davisson made no entries in
any of the research notebooks kept in the Bell Labs files. Figure 6

was at last able to exclaim,

“I finished the first draft of our paper
this morning. It is going to take a lot
of going over and revising ... I will
leave [the drawings] to Lester — and
also the thing is full of blanks in which
he will have to stick in the right num-
bers.”

A week later he made his final changes
before departing for Maine. Germer, too,
needed a break, and after finishing his
tasks he left on 14 August for a canoe trip
with several friends. The final copy was
sent to the Physical Review in August and
the article appeared in December.

The paper itself was a detailed, com-
prehensive report on experiments per-
formed, conclusions reached and ques-
tions left unanswered. One of the sig-
nificant features of the paper was its
thoughtful examination of the possible
ways of interpreting the systematic dif-
ferences between observed and calculated
electron wavelengths (either the sug-

gested ‘‘contraction factor” or an “index
of refraction” proposed by Carl Eckart,
A.L. Patterson, and Fritz Zwicky in in-
dependent responses to the Nature arti-
cle).11 Summarizing the evidence, the
paper concluded that of the 30 beams that
had been observed, 29 were adequately
accounted for by attributing wave prop-
erties to free electrons. It acknowledged,
however, that the wave assumption im-
plied the existence of eight additional
beams, which had not been observed.

The discrepancies between theory and
experiment, apparently fairly minor, that
Davisson and Germer recorded, evidently
did not reduce their fundamental belief
that free electrons behave like waves.
The physics community appears to have
concurred, for I have not found a single
voice raised in opposition. This may well
have been due as much to the success of
the earlier theory of wave mechanics and
the acceptance of a wave-particle duality
for light as to the force of the evidence

inherent in the paper itself.

This may be illustrated by some re-
marks made by prominent physicists
prior to the publication of the Phys. Rev.
article. In the reports and discussions of
the fifth Solvay Conference held in
Brussels in October 1927, Niels Bohr, de
Broglie, Born, Heisenberg, Langmuir and
Schrodinger all hailed the experiments of
Davisson and Germer (as described in the
Nature article) as being, in the words of
de Broglie, “very important results which
[appear] to confirm the general provisions
and even the formulas of wave mechan-
ics.”12 Bohr, speaking before the Inter-
national Congress of Physics assembled
in Como, Italy, on 16 September 1927,
drew upon these experiments in estab-
lishing his views on complementarity:

“. . . the discovery of the selective re-
flection of electrons from metal crys-
tals . . . requires the use -of the wave
theory superposition principle . . .
Just as in the case of light ... we are
not dealing with contradictory but
with complementary pictures of phe-
nomena.”13

Planck, addressing the Franklin Insti-
tute on 18 May 1927, even before he had
heard of the Davisson-Germer results,
stated about the electron: “[Its] motion
[in the atom] resembles ... the vibrations
of a standing wave . . . [Thanks] to the
ideas introduced into science by L. de
Broglie and E. Schrodinger, these prin-
ciples have already established a solid
foundation.”14 Yet in the same address
Planck stated that he was still (in 1927,
four years after the decisive Compton
experiments) reluctant to accept the
corpuscular implications for electromag-
netic radiation inherent in his own
quantum hypothesis! It appears that
physicists were willing to accept the ex-
perimental evidence for electron waves
almost before those experiments were
performed!

The world that is physics

Davisson and Germer succeeded where
others had failed. In fact, the others
mentioned above (Elsasser, Dymond,
Blackett, Chadwick and Ellis), who had
the idea of electron diffraction consider-
ably ahead of Davisson and Germer, were
not able to produce the desired experi-
mental evidence for it. G.P. Thomson,
who did find that evidence by a very dif-
ferent method, testified to the magnitude
of the technical achievement as follows:
“[Davisson and Germer’s work] was
indeed a triumph of experimental
skill. The relatively slow electrons
[they] used are most difficult to han-
dle. If the results are to be of any
value the vacuum has to be quite out-
standingly good. Even now [1961] . . .
it would be a very difficult experi-
ment. In those days it was a veritable
triumph. It is a tribute to Davisson’s
experimental skill that only two or
three other workers have used slow

PARTICLES AND QUANTA

331

New colatitude and azimuth curves. The black lines show the ap-
pearance of the colatitude (left) and azimuth (right) distributions of the
scattered electrons when Davisson took the curves to England in 1926.

The colored curves are from data taken after 6 January 1927, when the
first “quantum bump" was observed. The azimuth curves also confirm
the threefold symmetry of the nickel crystal. Figure 7

electrons successfully for this pur-
pose.”15

Davisson and Thomson shared in the
Nobel Prize for physics in 1937 for their
accomplishments. Germer and Reid, as
junior partners to Davisson and Thom-
son, did not share in the prize. Reid was
tragically killed in a motorcycle accident
shortly after his and Thomson’s definitive
papers appeared in 1928.

Davisson and Germer actively pursued
the topic of electron diffraction for about
three years after 1927, publishing, to-
gether and separately, about twenty more
papers on the subject; reference 16 gives
three of the most important. By the early
1930’s, both Davisson and Germer had
turned to new fields: Davisson to elec-
tron optics (including early television);
Germer to high-energy electron diffrac-
tion and later still to electrical contacts.
Davisson retired from Bell Labs in 1946
and spent the remaining twelve years of
his life in Charlottesville, Virginia, sum-
mering as usual in Maine. Germer re-
gained his interest in low-energy electron
diffraction in 1959-60, at which time he
and several co-workers at Bell Labs per-
fected a technique, eventually referred to
as the “post-acceleration” technique,17
which had been devised in 193418 and
then abandoned, by Wilhelm Ehrenberg.
With this work Germer was able to follow
up with great success the study of sur-
faces, to which he had been attracted in
his origipal work with Davisson; the field
of low-energy electron diffraction (LEED)
is now widespread and very active. Ger-
mer retired from Bell Labs in 1961 and
remained active in this “new” field and in
his favorite recreation, mountain climb-
ing, until his death in 1971.

In trying to answer the question of

“Why Davisson and Germer, and not
someone else?” one’s thoughts leap to
such things as the “luck” of the broken
tube in 1925 and the trip to England in
1926. Davisson and Germer themselves
freely admitted the key importance of
these events. But to dwell on them ex-
clusively would be a mistake. Neither of
these events would even have been re-
membered had they not been followed by
thorough, careful and creative experiment
and reflection. Perhaps of equal impor-
tance is the habit of attention to technical
detail established by Davisson in his stu-
dent days and extended in the long series
of Davisson-Kunsman and earlier Dav-
isson-Germer experiments. Another
important factor is the time for pure re-
search provided by Western Electric-Bell
Labs, and the technical support in areas
such as high vacua and electrical detection
techniques available at that industrial
laboratory.

All in all, this case history on the dis-
covery of electron diffraction appears to
illustrate the complex nature of the world
that is physics, the difficulty of singling
out any one factor as being responsible for
a great discovery, and the importance of
establishing and nurturing the ties that
bind together the generations of physi-
cists, as well as the physicists of each
generation.

References

References to correspondence, personal re-
marks and other archival material are docu-
mented in the author’s PhD dissertation, “C.J.
Davisson, L. H. Germer, and the Discovery of
Electron Diffraction,” University of Minne-
sota, 1973, available from Xerox University
Microfilms, 3000 North Zeeb Road, Ann Arbor,
Michigan 48106, Order No. 74-10 505.

1. C. J. Davisson, L. H. Germer, Phys. Rev.
30, 705 (1927).

2. US Reports 283, 665 (1931).

3. C. J. Davisson, L. H. Germer, Phys. Rev.
15, 330(1920).

4. C. J. Davisson, C. H. Kunsman, Science 54,
523 (1921).

5. M. Born, Nature 1 19, 354 (1927).

6. W. Elsasser, Naturwissenschaften 13, 711
(1925); E. G. Dymond, Nature 118, 336
(1926).

7. G. P. Thomson, A. Reid, Nature 119, 890
(1927).

8. C. J. Davisson, L. H. Germer, Nature 119,
558 (1927).

9. C. J. Davisson, Bell Lab. Record 4, 257
(1927).

10. C. J. Davisson, L. H. Germer, Phys. Rev.
29, 908 (1927).

11. C. Eckart, Proc. Nat. Acad. Sci. 13, 460
(1927); A. L. Patterson, Nature 120, 46
(1927); F. Zwicky, Proc. Nat. Acad. Sci. 13,
518 (1927).

12. L’lnstitut International de Physique Sol-
vay, Electrons et Protons: Rapports et
Discussions du Cinquieme Conseil de
Physique, Gauthier-Villars, Paris (1928),
pages 92, 127, 165, 173, 274, 288.

13. N. Bohr, Atomic Theory and the De-
scription of Nature, Macmillan, New York
(1934), page 56; italics supplied.

14. M. Planck, J. Franklin Inst. 204, 13
(1927).

15. G. P. Thomson, The Inspiration of
Science, Oxford U.P., London (1961); re-
printed by Doubleday, Garden City, New
York (1968), page 163.

16. C. J. Davisson, L. H. Germer, Proc. Nat.
Acad. Sci. 14, 317 (1928); Proc. Nat. Acad.
Sci. 14, 619 (1928); Phys. Rev. 33, 760
(1929).

17. A. U. MacRae, Science 139, 379 (1963).

18. W. Ehrenberg, Philosoph. Mag. 18, 878

(1934). □

332

HISTORY OF PHYSICS

1932— Moving into
the new physics

The exciting events of the early 1930’s raised high hopes

for progress in nuclear physics and, before the end of the decade,

had changed its pace, scale, cost and social applications.

Charles Weiner

In 1972 we celebrate the fortieth an-
niversary of the “annus mirabilis” of
nuclear and particle physics. Seen
from the perspective of the present,
the cluster of major conceptual and
technical developments of 1932 mark
that “marvelous” year as a very spe-
cial one. It began with Harold
Urey’s announcement in January
that he had discovered a heavy iso-
tope of hydrogen, which he called
"deuterium.” In February James
Chadwick demonstrated the exis-
tence of a new nuclear constituent,
the neutron. In April John
Cockcroft and E. T. S. Walton ach-
ieved the first disintegration of nu-
clei by bombarding light elements
with artificially accelerated protons.
In August Carl Anderson’s photo-
graphs of cosmic-ray tracks revealed
the existence of another new particle,
the positively charged electron, soon
to be called the “positron.” And
later that summer Ernest Lawrence,
Stanley Livingston and Milton White
disintegrated nuclei with the cyclo-
tron, an instrument that would gen-
erate almost 5-million electron volts
by the end of that eventful year.

New particles, new constituents of
the nucleus and powerful new techni-
ques for probing its structure — they
all provided a wealth of fresh challen-
ges and opportunities for theory and
experiment. Physicists who remember
the excitement of those days some-
times sound as if they were relishing an
excellent wine when they smile and
comment: “It was a great year.”

What were the circumstances and

Charles Weiner is professor of History of
Science and Technology at MIT.

the immediate impact of these events?
Was their significance recognized at
the time? And what effect did they
have in the decade that followed?
Historians ask such questions in the
hope that the answers may reveal more
about the nature of scientific activity
and the processes and consequences of
scientific change than is evident in a
mere listing of key discoveries. Parti-
cularly interesting are the social
structures and processes that helped
create the environment for doing nu-
clear physics and influenced its rela-
tionships to the scientific community
and to the larger society in which it
functions. The events of 1932 helped
open new fields of research and led to
important changes in the pace, scale,
cost, organization and style of experi-
mental physics research. In addition,
the rapid growth of nuclear physics
gave rise in the 1930’s to public expec-
tations of applications, expectations
that were to be fulfilled in unanticipat-
ed ways before the end of the decade.

These developments are being illu-
minated through historical documenta-
tion and research studies underway at
the American Institute of Physics Cen-
ter for History and Philosophy of Phys-
ics. Here I shall draw on some of the
results to provide glimpses of the cir-
cumstances of the 1932 discoveries and
the immediate effect on some of the
discoverers and their colleagues.
Wherever possible, these individuals
will speak for themselves, in excerpts
from the letters they exchanged or
from interviews I have more recently
conducted with several of them. I
shall also sketch the effect of the 1932
events on the growth of nuclear-physics
research in the US in the 1930’s and
indicate briefly the special role of Law-

PHYSICS TODAY / MAY 1972

rence’s Berkeley laboratory: We shall
see that one of the most striking effects
of the “annus mirabilis” was its impact
on the social organization and support
of academic research.

These glimpses cannot provide a full
or balanced picture, nor even a chro-
nological listing of the many intercon-
nected conceptual, technical and social
factors involved. But they do offer some
insight into the spirit of the times.

News from the US

The stage was set at the very begin-
ning of 1932, and the action that was
soon to unfold into the dramatic devel-
opments of that year was already un-
derway. Some of the highlights of the
developing situation in the US are seen
in a letter written on 8 January by Jo-
seph Boyce of Princeton to John
Cockcroft, his friend and former col-
league at the Cavendish Laboratory in
Cambridge:

“I have just been on a very brief
visit in California and thought you
might be interested in a brief report
on high voltage work there and in
the eastern US as well. At Pasade-
na [Charles] Lauritsen continues
work with his 700 000 volt x-ray
tube. ... He is now waiting for the
GE to furnish him other transfor-
mers to go to still higher voltages.
[Robert] Millikan and Anderson are
working a Wilson chamber between
the poles of a very large magnet and
are obtaining cosmic ray recoil and
disintegration tracks whose curv-
atures can be measured. . . . Ever-
yone seems most enthusiastic about
[the results], even people outside
Pasadena. Some of the photographs
show simultaneous ejection of ( + )
and (-) particles of high speed, as if

PARTICLES AND QUANTA

333

both a proton and an electron were
knocked out from a nucleus by the
cosmic ray. . . . With that and the
high voltage developments every-
where it looks as if cosmic ray work
will become a laboratory problem for
a while rather than a mountain-
climbing excuse.”1

Boyce’s news about the Caltech cos-
mic-ray photographs and the possible
nuclear reactions involved had in fact
already been brought to Cambridge by
Millikan, who was visiting at the Ca-
vendish Laboratory in November 1931
when he received copies of the photo-
graphs in a letter from Anderson.
After describing the puzzling tracks —
for example, “a positive particle mov-
ing downward or an electron moving
upward” — Anderson concluded: “A
hundred questions concerning the de-
tails of these effects immediately come
to mind. ... It promises to be a fruitful
field and no doubt much information
of a very fundamental character will
come out of it. . . ,”2

The fundamental information did
“come out” in August 1932, when An-
derson identified the curious tracks in
some new photographs as evidence of a
“positively-charged particle compara-
ble in mass and in magnitude of charge
with an electron.”3

Boyce’s January 1932 letter went on:

“But the place on the coast where
things are really going on is Berk-
eley. Lawrence is just moving into
an old wooden building back of the
physics building where he hopes to
have six different high-speed particle
outfits. One is to move over the
present device by which he whirls
protons in a magnetic field and in a
very high frequency tuned electric
field and so is able to give them

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John Cockcroft and George Gamow (right) work on a nuclear-physics problem in December
1 933. Gamow’s theoretical ideas of 1 928 spurred on the building of the Cockcroft-Walton
accelerator, which in 1 932 achieved the first nuclear disintegration by artificially accelerated
particles. In a letter written 29 March 1934, Gamow exchanges the latest news with
Cockcroft. Cockcroft's minuscule handwriting and Gamow's unique English spelling were
notorious but apparently did not interfere with communication between the two men.

(Photo, by K. T. Bainbridge, from Niels Bohr Library; original letter in Churchill College
Library, Cambridge.)

velocities a little in excess of a mil-
lion volts. With this he has already
had proton currents of the order of
10 9 amps. . . . Then there is the Hg
ion outfit. . . . This has already given
Hg ions in excess of a million volts,
by the use of about 50000 volts high
frequency. . . . Several more units
can be added to it, all driven by a
master oscillator. Then a similar
device with higher applied voltages
and longer electrodes to use with
protons. The fourth is a whirling
device for protons in a magnet with
pole pieces 45 inches in diameter,
with which he hopes for at least 3
million volts, perhaps more. . . .
Then a small tesla-coil x-ray outfit
is already installed, and the remain-
ing room is reserved for a Van de
Graaff electrostatic generator. On
paper this sounds like a wild damn
fool program, but Lawrence is a very
able director, has many graduate
students, adequate financial back-
ing, and in his work so far with pro-
tons and mercury ions has achieved
sufficient success to justify great
confidence in his future. . .

Back in the east [Merle] Tuve at
Washington [Carnegie Institution] is
working on the development of tubes
to stand high voltages, and has or-
dered a six foot sphere to build a
one-ball Van de Graaff outfit for
about 3 million [volts]. I think I
sent you clippings about Van’s [Rob-
ert Van de Graaff ’s] own results and
plans. . .

On the way west I stopped at New
Orleans for the Physical Society
meeting. The most interesting
paper was Urey’s on the hydrogen
isotope. The spectroscopic evidence

alone, as reported in the abstract is
quite convincing, but [Walker]
Bleakney in our [Princeton] labora-
tory has been able to confirm it with
a mass spectrograph. . -”1

Discovery of the neutron

All of these developments described
by Boyce were of great interest to the
physicists in the Cavendish Laborato-
ry, where work aimed at probing the
nature and structure of the nucleus
had been pursued under Ernest Ruth-
erford for more than a decade. These
efforts began to pay off dramatically
early in 1932. 4 James Chadwick had
been searching for the neutron ever
since Rutherford had suggested in his
Bakerian Lecture in 1920 that such a
particle might exist. He followed up
observations made in 1930 by two Ger-
man scientists, Walther Bothe and H.
Becker, which were subsequently ex-
tended at the end of 1931 in Paris by
Frederic and Irene Joliot-Curie.
Chadwick’s own recollections of the
circumstances provide some of the fla-
vor of the event:

“One morning I read the commun-
ication of the Curie-Joliots in the
Comptes Rendus, in which they re-
ported a still more surprising prop-
erty of the radiation from beryllium,
a most startling property. Not
many minutes afterwards [Norman]
Feather came to my room to tell me
about this report, as astonished as I
was. A little later that morning I
told Rutherford. It was a custom of
long standing that I should visit him
about 11 a.m. to tell him any news of
interest and to discuss the work in
progress in the laboratory. As I told
him about the Curie-Joliot observa-

tion and their views on it, I saw his
growing amazement; and finally he
burst out ‘I don’t believe it.’ Such
an impatient remark was utterly out
of character, and in all my long asso-
ciation with him I recall no similar
occasion. I mention it to emphasize
the electrifying effect of the Curie-
Joliot report. Of course, Rutherford
agreed that one must believe the ob-
servations; the explanation was quite
another matter.

It so happened that I was just
ready to begin experiment, for I had
prepared a beautiful source of polo-
nium from the Baltimore material
[used radon tubes brought back by
Feather]. I started with an open
mind, though naturally my thoughts
were on the neutron. I was reasona-
bly sure that the Curie-Joliot obser-
vations could not be ascribed to a
kind of Compton effect, for I had
looked for this more than once. I
was convinced that there was some-
thing quite new as well as strange.
A few days of strenuous work were
sufficient to show that these strange
effects were due to a neutral particle
and to enable me to measure its
mass: the neutron postulated by

Rutherford in 1920 had at last re-
vealed itself.”5

Chadwick’s letter announcing the dis-
covery was to appear in Nature on 27
February, 1932® and on 24 February he
sent proofs of the letter to Niels Bohr
in Copenhagen. Bohr then invited
Chadwick to come and discuss his
work at the small informal conference
that had been planned for the second
week of April at the Copenhagen inst-
itute.7 These annual week-long con-
ferences had been started in 1929 and

-

PARTICLES AND QUANTA

335

Participants in the April 1932 conference

at Niels Bohr's Institute of Theoretical
Physics in Copenhagen. Seated in the first
row are Leon Brillouin (left), Lise Meitner
and Paul Ehrenfest. Seated behind and to
the right of Ehrenfest is H. A. Kramers.

The first six people, from the left, standing
along the wall are Werner Heisenberg, Piet
Hein, Niels Bohr, Leon Rosenfeld, Max
Delbruck and Felix Bloch. Seated second
from the right in the last row is P. A. M.
Dirac, with R. H. Fowler on his right. Other
visitors to Copenhagen in the group include
Walter Heitler, Karl von Weiszacker, Guido
Beck and C. G. Darwin. (Photo: Niels
Bohr Institute, Copenhagen.)

they brought together physicists from
many different countries to discuss, as
Bohr put it, “actual atomic problems.”

Chadwick was unable to attend the
meeting, but R. H. Fowler of Cam-
bridge was present and provided an
up-to-the-minute account of the exper-
imental work underway by Chadwick,
Feather and P. I. Dee in their follow-
up of Chadwick’s discovery. The con-
ference was truly international: The
22 foreign physicists were from 17 inst-
itutions in nine countries. Among the
participants were C. G. Darwin, Max
Delbruck, Paul Ehrenfest, P. A. M.
Dirac, R. H. Fowler, Werner Heisen-
berg, Walter Heitler, H. A. Kramers
and Lise Meitner.8 Bohr’s personal
style of thinking out loud set the tone
for the Copenhagen conferences and
stimulated a lively exchange of infor-
mation, ideas and interpretations.
The neutron, like the other topics dis-
cussed at the meeting, found a place in
the parody of Faust written and per-
formed there by some of the parti-
cipants:

“Now a reality, /Once but a vision.

W’hat classicality, /Grace and preci-
sion!

Hailed with cordiality, /Honored in

song,

Eternal neutrality / Pulls us along! ”9

In June, only two months after the Co-
penhagen conference, Heisenberg sub-
mitted the first in a three-part series of
papers that incorporated the neutron
in a theory of the nucleus to demon-
strate that quantum mechanics could be
applied to many existing nuclear
problems.10 That summer he was a
lecturer at the University of Michigan’s
annual summer schools in theoretical

physics, which attracted physicists
from all over the US and Europe. In
November Samuel Goudsmit wrote to
Bohr from Michigan, commenting on
Heisenberg’s lectures:

“We followed with great interest
his new ideas about the nucleus but
everyone feels that there still are
great difficulties. It is strange and
regrettable that the discovery of the
neutron did not give some more fer-
tile clues for progress. In many res-
pects the situation has not changed
much from what it was at the Rome
meeting a year ago, except that the
difficulties can now be formulated
more sharply. I have been playing
around with nuclear magnetic mo-
ments, but none of my speculations
yielded any results certain enough to
communicate.”11
Bohr replied:

’’Not least in connection with the
[difficulties of relativistic quantum
mechanics] we have all been very in-
terested [in] the problem of nuclear
constitution and the possible clue to
this problem offered by the discovery
of the neutron. Still I quite agree
with you as regards the very prelimi-
nary character of any attempt hith-
erto made to attack the problem on
such lines.”12

An acceptable theory of the nucleus
was still beset with difficulties by the
end of 1932, but the neutron did at-
tract theorists to nuclear problems be-
cause it provided fresh challenges and
possibilities for theory. One senior nu-
clear theorist recently explained: “I
went into nuclear physics only after
1932 . . . after the discovery of the neu-
tron in 1932, it was in a general way
clear what had to be done ... I cannot
invent something out of nothing...”
Another recalled: “For me [nuclear
physics] started with Heisenberg’s
paper . . . [he] pointed out that now
that the neutron has been discovered,
one can think of starting a theory of
the nucleus. This impressed me very
much.”13

Accelerators attack the nucleus

Other news from the Cavendish fol-
lowed on the heels of the discovery of
the neutron. On 21 April 1932, about
a week after the neutron was discussed
at the Copenhagen meeting, Ruther-
ford wrote to Bohr:

“I was very glad to hear about you
all from Fowler when he returned to
Cambridge and to know what an ex-
cellent meeting of old friends you
had. I was interested to hear about
your theory of the Neutron. . . .

It never rains but it pours, and I
have another interesting develop-
ment to tell you about of which a
short account should appear in Nat-
ure next week. You know that we
have a High Tension Laboratory

where steady D.C. voltages can be
readily obtained up to 600 000 volts
or more. They have recently been
examining the effects of a bombard-
ment of light elements by pro-
tons. ...”

Rutherford went on to describe the
work of Cockcroft and Walton in which
they achieved the first artificial nu-
clear disintegrations with the high-vol-
tage accelerator that they had been de-
veloping at the Cavendish since 1929.
He concluded:

“I am very pleased that the energy
and expense in getting high poten-
tials has been rewarded by definite
and interesting results. . . . You can
easily appreciate that these results
may open up a wide line of research
in transmutation generally.”14
Bohr’s response reveals that he fully
shared Rutherford’s evaluation of the
significance of this latest development:

“By your kind letter with the in-
formation about the wonderful new
results arrived at in your laboratory
you made me a very great pleasure
indeed. Progress in the field of nu-
clear constitution is at the moment
really so rapid, that one wonders
what the next post will bring, and
the enthusiasm of which every line
in your letter tells will surely be
common to all physicists. One sees
a broad new avenue opened, and it
should soon be possible to predict
the behavior of any nucleus under
given circumstances.”15
Thirty-five years later, Cockcroft
warmly recounted the atmosphere in
the Cavendish when they achieved
their results:

“It was extremely exciting to see
the alpha particles in this transmu-
tation. The first thing we did was to
call up Rutherford on the laboratory
exchange and invite him to come
down and have a look at the scintil-
lations, which he did. He, of course,
was very excited about it.”16
The story was soon carried in newspap-
ers throughout the world, reviving al-
chemical dreams and hopes for new en-
ergy sources. For example, The New
York Times carried articles on the
Cockcroft- Walton work, with the fol-
lowing headlines: 1 May, “Atom
Torn Apart with Energy Rise;” 3 May,
“Hail New Approach to Energy of
Atom;” 3 May, “Value Put in Energy
Gain;” 4 May, “Atomic Energy;” and 8
May, “Atom Bombarders.”

What of the reaction within the
physics community? Cockcroft re-
called the rapid response that “came
from Berkeley and from Tuve’s lab in
Washington, where they had all been
working on development of high-vol-
tage equipment, such as the cyclotron
or the Van de Graaff machine, toward
just this kind of experiment.”16 On 20
August 1932, Lawrence wrote to

336

HISTORY OF PHYSICS

Cockcroft and Walton:

“I want to thank you very much
for the reprints of your epoch making
experiments on the disintegration of
the elements by high velocity pro-
tons, and I hope you will continue to
send me accounts of your work in the
future. Under separate cover I am
sending you reprints of the work of
myself and my coworkers on meth-
ods for the acceleration of ions,
which you may find of some interest.

At the present time we are at-
tempting to corroborate your experi-
ments using protons accelerated to
high speeds by our method of multi-
ple acceleration. We have some evi-
dence already of disintegration,
though as yet we can not be certain.
Unfortunately our beam of protons is
not nearly as intense as yours — al-
though of higher voltage. Whenever
we obtain some reliable results, of
course, we will let you know prompt-
ly.”17

Stanley Livingston recently recalled
the Berkeley response:

“With the 11-inch [cyclotron] we
had resonant particles of full energy
in a collector cup at the edge of the
pole. Our first publication was sent
in to the Physical Review on Febru-
ary 20th, 1932 reporting 1 200 000
volts. Cockcroft and Walton’s paper
came out later that spring and
showed that they had disintegrated
nuclei with even lower energies.

Well, we weren’t ready for experi-
ments yet. We didn’t have the in-
struments for detection. I had built
the machine but had not included
any devices for studying disintegra-
tions. So we had to rebuild it.
Now, Milton White was a student
at that time, following right along
behind me. He joined with me that
spring in helping to rebuild the ma-
chine, and Lawrence also put in an
emergency call to his friend Don
Cooksey at Yale, who came out.
Franz Kurie, a graduate student,
also came out with Cooksey for the
summer. Meanwhile we re-
equipped the chamber with a target
mounted inside where it would be
hit by the beam, and a thin-foiled
window on the side where we could
mount counters. I think the first
devices used for detecting the pro-
duct particles were Geiger point
counters. We set the threshold low
so that they wouldn’t trigger with
x-rays or ultra-violet and they would
count with particles. It wasn’t long
before we started to observe disinteg-
rations, too. . . ,”18

The exciting developments of 1932
stirred new interest in nuclear physics
and the pace of activity began to
quicken as the new techniques and
concepts were put into action. The
need for personal visits to the laborato-

ries involved was obvious, if one was to
keep abreast of the new work. At the
beginning of 1933, Cockcroft planned
to visit the US to study the work of
Tuve, Lauritsen and Lawrence and to
discuss with them the future of their
various methods of nuclear disintegra-
tion. Applying for a travel grant for
Cockcroft’s trip, Rutherford wrote to
the Rockefeller Foundation: “During
the last year we have had visits from a
number of workers interested in this
field, and have given them as much in-
formation as we possess on our own
methods.”19 He stressed that now it
was equally valuable for the Cavendish
workers to have similar first hand know-
ledge of work underway in US Labora-
tories.

Before Cockcroft’s June trip regular
letters kept physicists at the various
institutions informed of one another’s
techniques and results. Lawrence’s
enthusiasm was evident when he wrote
to Cockcroft at the beginning of June
1933: “We have been having a most
exciting month in the laboratory. We
have obtained so many disintegration
effects that it is impossible for me to
keep them all in mind. I am almost
bewildered by the results. I will men-
tion only a few as I will be seeing you
soon. . . ,”20

Cockcroft later recalled his impres-
sions of that visit to the Berkeley lab-
oratory:

“It was really interesting to see it
actually in operation after having
read so much about it in the jour-
nals. I was very much impressed by
the way of working; to see the seal-
ing-wax and string way of working on
the cyclotron, which functioned for
very short periods of time. They
had a two-shift system, one shift
doing the experiments, the other
shift keeping the cyclotron going.
And as soon as a leak developed,
the maintenance shift would dash in
and the experiment shift would re-
tire backwards. A highly organized
system.”16

Just before Cockcroft left for the US,
and a little more than a year after
Rutherford had written Bohr that the
Cockcroft-Walton results “may open
up a wide line of research,” Rutherford
wrote to Gilbert N. Lewis, the re-
nowned physical chemist at Berkeley,
who had supplied him with heavy hy-
drogen for use as a projectile in the Ca-
vendish accelerators. The aging dean
of nuclear physics was enthusiastic
about the new prospects for research in
the field in which he had pioneered for
many decades:

“I was delighted to receive your
concentrated sample of the new hy-
drogen isotope in good shape, and we
shall certainly take an early opportu-
nity of examining its effects in our
low voltage apparatus which Dr. Oli-

phant and I have been using the past
year.

I have been enormously interested
in your work of concentration of the
new isotope with almost unbelieva-
ble success. I congratulate you and
your staff on this splendid perfor-
mance. I can appreciate the ex-
traordinary value of this new ele-
ment in opening up a new type of
chemistry. If I were a younger man
I think I would leave everything else
to examine the effects produced by
the substitution of H2 for H1 in all
reactions.

Next, I should like to congratulate
Lawrence and his colleagues for the
prompt use they have made of this
new club to attack the nuclear
enemy. Cockcroft showed me the
letter of Lawrence giving his prelimi-
nary results which are very exciting.
These developments make me feel
quite young again as in the early
days of radioactivity when new
discoveries came along almost every
week, for it is a double scoop not
only to prepare this new material
but also to have the powerful method
of Lawrence to examine its effects on
nuclei. I wish them every success in
their work and as soon as we can ar-
range it, I will try out the effects we
can observe at our low voltages.”21
In October 1933 the Solvay Congress in
Brussels brought together most of the
major participants in the burgeoning
field, and a year later, in London, an-
other international conference on nu-
clear physics was held. By that time
there were many more important new
developments to discuss, including En-
rico Fermi’s theory of beta decay, the
discovery of artificially induced rad-
ioactivity by the Joliot-Curies in Paris,
and the technique of neutron bombard-
ment to produce artificial radioactiv-
ity, which was systematically applied
and developed by Fermi’s group in
Rome.

An American who attended the Lon-
don conference was Frank Spedding, a
former student of Lewis. His com-
ments, in a letter to Lewis in Decem-
ber 1934, characterize the rapid pace of
nuclear physics in the aftermath of the
1932 events, and show the reaction of a
nonspecialist:

“There was also a symposium on
nuclear physics. This field is mov-
ing so rapidly that one becomes
dizzy contemplating it. With talk of
the experimental properties of H3,
He3, He5, the new artificial radioac-
tive elements, the neutron and posi-
tron, and the predicted properties of
the neutrino and proton of minus
charge, one who has been brought up
on the old naive picture of protons
and electrons in the nucleus feels
bewildered. I managed to attend a
few of these sessions and found them

PARTICLES AND QUANTA

337

E. T. S. Walton and John Cockcroft (right)
flank Ernest Rutherford in a 1 932 photograph
taken outside the Cavendish, after their
accelerator had disintegrated nuclei by
bombardment with protons. (Photo: UK
Atomic Energy Authority.)

James Chadwick, working at the Cavendish
Laboratory, had been searching for evidence
of the neutron ever since Ernest Rutherford’s
suggestion, in 1920, that such a particle
might exist. In 1 932, about the time of this
photograph, his efforts became successful.
(Photo: Meggers Collection, Niels Bohr
Library.)

extraordinarily interesting. There
was one rather amusing incident that
occurred here. Prof. Born had pre-
pared a rather involved paper on the
quantum theory of the nucleus. (An
extension of Dirac’s theory of the el-
ectron.) He wrote the paper long-
hand labelling it “For the Confer-
ence on Nuclear Physics.” He made
his “n” ’s and “u” ’s much alike so
that his stenographer in copying it
wrote “For the Conference on Un-
clear Physics.”22

Indications of growth

One thing was clear about nuclear
physics in the early 1930’s: It was
growing more rapidly than any other
field of physics. This was especially
true in the US, which provided a parti-
cularly fertile environment for the new
and growing field to take root. The ef-
fect of the annus mirabilis can be
clearly seen in the jump in nuclear-
physics publications in The Physical
Review between 1932 and 1933. The
results of a study by Henry Small at
the AIP Center for History and Philoso-
phy of Physics show that in The Physi-
cal Review, nuclear-physics papers,
letters and abstracts increased from 8%
of the publications in 1932 to 18% in
1933 and reached 32% by 1937. A
further examination of the dramatic
increase in the number of nuclear-
physics publications in The Physical
Review between 1932 and 1933 shows
that 42% of the increase was due to
publications involving the neutron and
18% to those involving disintegration
by protons. Publications from Berkeley
alone accounted for 38% of the total in-
crease in nuclear-physics papers bet-
ween 1932 and 1933. 23

While the total number and propor-
tion of nuclear-physics papers was ris-
ing, the number of nuclear-physics
papers that acknowledged funding was
increasing even faster. In 1930, before
the annus mirabilis, nuclear-physics
papers constituted a very minor per-
centage of the papers in The Physical
Review and a similarly small percen-
tage of the funded papers. By 1935,
however, when nuclear physics ac-
counted for 22% of all papers in The
Physical Review, fully 46% of the total
funded papers were nuclear. And by
1940, when 34% of The Physical Re-
view papers were in nuclear physics,
they accounted for 55% of the funded
papers. Clearly, nuclear physics was
not only growing but also becoming a
relatively heavily funded research
subject. In fact, by 1939 fully one
third of the nuclear-physics papers
were being funded.

Another indication of the growth of a
field is the number of new physics
PhD’s whose dissertation research is on
a topic within the field. Here again
nuclear physics showed an increase in
the US from 2 new PhD’s in 1930 to 41
in 1939. It was the only field of phys-
ics to increase steadily through the de-
cade, and from 1937 on more new
PhD’s specialized in nuclear physics
than in any other single field.

Of course, the growth of nuclear
physics in the 1930’s was not due solely
to the discoveries of 1932. But these
discoveries did help to focus the atten-
tion of a significant part of the physics
community on nuclear phenomena and
on the new possibilities for fruitful re-
search in that field, possibilities which
were expanded yet further with the de-
velopment, availability and increasing-

Berkeley cyclotrons. Lefthand photo shows
chamber of the 1 1 -inch cyclotron. I n early
1932, Ernest Lawrence and M. Stanley
Livingston achieved a 10 '9-ampere, 1.22-
MeV proton beam; later experiments with
this chamber confirmed the artificial
disintegration of lithium that Cockcroft and
Walton had observed at lower energies.

The 60-inch Berkeley cyclotron (right) was
built for medical applications. This 1 938
photograph shows Luis Alvarez astride the
magnet-coil tank, Edwin McMillan on the
"D” stem casing and, standing (left to right),
Don Cooksey, Dale Corson, Lawrence,

Robert Thornton, John Backus and Winfield
Salisbury. (Photos: Lawrence Radiation
Laboratory.)

ly productive use of particle accelera-
tors. These instruments became cen-
tral to experimental work at a number
of new research centers that began to
flourish during the period.

Special role of Berkeley

Because Berkeley, and particularly
Lawrence’s radiation laboratory there,
played such a major role in these
developments, let us take a brief
glimpse into the Berkeley scene in the
1930 s. Clearly the Berkeley work was
very important in 1932, and it account-
ed for a large part of the field’s subse-
quent productivity in the US.
Throughout the 1930’s Berkeley not
only produced more nuclear-physics
papers and PhD’s than other US inst-
itutions but also had the lion’s share of
funded nuclear research. These statis-
tics, however, are only a part of the
story, for Berkeley also played a key
social role in developing the entire field
of nuclear physics internationally.24

Berkeley was the home of the cyclo-
tron, the instrument that became cen-
tral to nuclear physics research as it
took root in more and more institutions
throughout the world in the 1930’s.
The early 11 -inch model, which first
accelerated protons to energies of 1.2
million electron volts by the beginning
of 1932 and achieved nuclear disinteg-
rations later that year, had been made
possible by a grant of $500 from the
National Research Council of the Na-
tional Academy of Sciences in the
spring of 1931. By the spring of 1940
Lawrence had obtained a grant from
the Rockefeller Foundation for more
than one million dollars toward the
cost of creating a 100-million volt cy-
clotron. In the intervening years —
aided by grants from the University of

California, the Research Corporation,
the Chemical and Macy Foundations,
the US Works Progress Administra-
tion (WPA), as well as individual do-
nors— several generations of cyclotrons
of steadily increasing energy and wide
applications had been developed at
Berkeley by Lawrence and the team he
had assembled there.

The cyclotron had proved to be an
excellent instrument for particle-scat-
tering experiments and an unsurpassed
producer of powerful neutron sources
that could make a large variety of new
isotopes, thus providing previously
unavailable data essential for a fuller
understanding of nuclear structure.
These unstable isotopes were also
used for therapeutic medical applica-
tions and as tracers in pioneering
studies of chemical and biological pro-
cesses. The unique role of the cyclo-
tron as a producer of isotopes began in
1934, after the Joliot-Curies discovered
artificially induced radioactivity.
Later that year Fermi’s group in
Rome demonstrated induced radioac-
tivity by neutron bombardment. The
Berkeley cyclotron was soon at work
systematically producing artificially
radioactive isotopes of a number of el-
ements. Lawrence’s production of a
radioisotope of sodium in 1934 was
especially significant because of its po-
tential application to medical therapy.

The potential biological and medical
applications helped to create interest
in and financial support for the subse-
quent development of cyclotrons at
Berkeley and at other places. During
1935 a number of institutions started
to build cyclotrons because they recog-
nized that it was a major tool for nu-
clear studies. At several of these pla-
ces—for example, Bohr’s institute in

A

PARTICLES AND QUANTA

339

Copenhagen where George de Hevesy
was pursuing his tracer studies, the
University of Rochester where the
physics department was headed by Lee
DuBridge and the University of Michi-
gan where Harrison Randall was de-
partment chairman — the cyclotron pro-
jects were proposed and financed as
part of planned collaborative research
efforts involving the physics, medicine
and biology departments. At Berk-
eley, such joint efforts were wholehear-
tedly pursued and were immensely
strengthened when the physician John
Lawrence arrived from Yale in the
mid- 1930’s to collaborate with his
brother and others in a full medical
program involving not only isotopes
but also experiments in the use of neu-
tron beams for cancer therapy. Radi-
ochemistry also blossomed at Berkeley
where strong ties existed between the
physics and chemistry departments.

Recognition of the role of the cyclo-
tron in physics, chemistry, biology and
medicine resulted in a proliferation of
the instruments at institutions through-
out the world in the late 1930’s, and
almost all of these projects depended
on assistance from the Berkeley ex-
perts. Detailed technical information
and advice was communicated through
a lively network of personal letters, cir-
culation of unpublished technical me-
moranda and progress reports, personal
visits, and exchange of personnel. Don
Cooksey, who played a key role as the
Berkeley hub of this international in-
formal communication network, jok-
ingly referred to it in June 1938 as the
“Cyclotron Union of the World.”25 At
that time Berkeley -trained physicists
were building cyclotrons in Copenha-
gen, Stockholm, Paris, Cambridge,
Liverpool, Tokyo, and at more than a
dozen US institutions. The Berkeley
radiation laboratory played a key role
as an international information center,
a training school, a supplier of cyclo-
tron-produced radioactive materials for
use in other laboratories, and a source
of skilled physicists who were available
to help other institutions enter the cy-
clotron field. Thus the impact of Law-
rence’s laboratory transcended the im-
portant results being obtained in Berk-
eley and had a tremendous multiplier
effect on the entire field in the 1930’s.

I have described some of the events
of 1932 and the immediate responses of
some of the participants. It was clear
to them that the new developments
would open up an exciting period for
fruitful research in nuclear physics.
The field did flourish in the following
years and by the mid- 1930 ’s was firmly
established in a number of new centers
of nuclear research.

In March 1972 champagne toasts
were drunk in Batavia, Illinois to cele-
brate the achievement of accelerating
protons to record energies of 200 GeV
through the four-mile circumference of

the giant new accelerator there. It was
a fitting observance of the 40th anni-
versary of the “annus mirabilis” of 1932,
and makes one wonder how soon we
might see another “marvelous” year
and what its impact may be on physics
and society in the decade that follows.

* * *

The location and study of historical mater-
ials used in this article have been supported
by grants from the National Science
Foundation and the John Simon Guggen-
heim Memorial Foundation, and have been
greatly facilitated by the information re-
sources of the AIP Niels Bohr Library. Per-
mission to use and quote archival materials
and oral history interviews was kindly
granted by the appropriate institutions and
individuals cited. The author is grateful for
this assistance.

References

1. J. Boyce to J. Cockcroft, 8 January 1932,
Sir John Cockcroft Papers, Churchill
College Library, Cambridge, UK.

2. C. D. Anderson to R. A. Millikan, 3 No-
vember 1931, Robert A. Millikan Pap-
ers, California Institute of Technology
Archives, Pasadena. For Millikan’s ac-
count of his talks in Europe about the
photographs, see R. A. Millikan, Elec-
trons (+ and -J, Protons, Photons,
Neutrons and Cosmic Rays (Chicago,
1935), pages 327-330. The reaction of
some European physicists to these talks
is documented and analyzed in N. R.
Hanson, The Concept of the Positron
(Cambridge, UK, 1963), page 139-142,
216-217.

3. C. D. Anderson, Science 76, 238-239, 9
September 1932.

4. Some of the 1932 nuclear events are also dis-
cussed in C. Weiner, “Institutional Settings
for Scientific Change: Episodes from the His-
tory of Nuclear Physics,” in A. Thackray and
E. Mendelsohn, eds., Science and Values
(Humanities Press, N.Y., 1972).

5. J. Chadwick, “Some Personal Notes on
the Search for the Neutron,” Proceed-
ings of the 10th International Congress
of the History of Science, Ithaca, 1962
(Paris, 1964), page 161.

6. J. Chadwick, “On the Possible Existence
of the Neutron,” Nature 129, 312, 27 Fe-
bruary 1932.

7. J. Chadwick to N. Bohr, 24 February
1932, and N. Bohr to J. Chadwick, 25
March 1932, Niels Bohr Papers, Niels
Bohr Institute, Copenhagen. The Bohr
Papers have been microfilmed by The
American Physical Society-American
Philosophical Society project on Sources
for History of Quantum Physics, and
the films are deposited at the American
Philosophical Society, Philadelphia;
at the Bancroft Library, University of
California, Berkeley and at the AIP
Niels Bohr Library, New York.

8. Information on the conferences is availa-
ble in the Niels Bohr Institute adminis-
trative archive, Copenhagen.

9. Translation by Barbara Gamow in
George Gamow, Thirty Years That
Shook Physics, Doubleday, New York
(1966), page 214.

10. For a full discussion of Heisenberg’s
treatment of the neutron, see J.
Bromberg, “The Impact of the Neutron:
Bohr and Heisenberg,” in Historical
Studies in the Physical Sciences, Vol. 3
(1971), page 307-341.

11. S. Goudsmit to N. Bohr, 4 November

1932. Niels Bohr Institute administra-
tive archive, Copenhagen.

12. N. Bohr to S. Goudsmit, 28 December

1932, Niels Bohr Institute administra-
tive archive, Copenhagen.

13. Interviews conducted in connection with the
joint AIP-American Academy of Arts and
Sciences conferences on the history of nu-
clear physics held in May 1967 and May
1969. The proceedings and abstracts of the
interviews are in Exploring The History of
Nuclear Physics, AIP Conference Proceed-
ings 7 (1972).

14. E. Rutherford to N. Bohr, 21 April 1932,
Niels Bohr Papers, Niels Bohr Institute,
Copenhagen.

15. N. Bohr to E. Rutherford, 2 May 1932,
Rutherford Papers, Cambridge Univer-
sity Library, Cambridge, UK.

16. Interview with J. Cockcroft by C. Wein-
er, 28 March 1967, Oral History Collec-
tion, AIP Niels Bohr Library, New
York.

17. E. Lawrence to J. Cockcroft and E. T.

S. Walton, 20 August 1932, Cockcroft
Papers, Churchill College Library, Cam-
bridge, UK.

18. Interview with M. S. Livingston by C.
Weiner, 21 August 1967, Oral History
Collection, AIP Niels Bohr Library.

19. E. Rutherford to W. Tisdale, 6 March

1933, Cockcroft Papers, Churchill Col-
lege Library, Cambridge, UK.

20. E. Lawrence to J. Cockcroft, 2 June

1933, Cockcroft Papers, Churchill Col-
lege Library, Cambridge, UK.

21. E. Rutherford to G. N. Lewis, 30 May 1933,
G. N. Lewis Papers, Bancroft Library, Uni-
versity of California, Berkeley.

22. F. Spedding to G. N. Lewis, 1 December

1934, Lewis Papers, Berkeley.

23. The data are drawn from the statistical
study of the physics journal literature con-
ducted by H. Small with the assistance of D.
Schreibersdorf at the AIP Center for His-
tory of Physics under a National Science
Foundation grant. Work-in-progress re-
ports were presented by Small at the His-
tory of Science Society annual meetings in
1970 and 1971 and are in the AIP archives.

24. The brief sketch here is based on archi-
val materials from the Lawrence Radia-
tion Laboratory, the Cavendish Labora-
tory and the Bohr Institute in Copen-
hagen; physics-department files at sev-
eral US universities; Herbert Childs’s
biography of Lawrence, An American
Genius (Dutton, New York, 1968); and on
historical accounts of the cyclotron such
as those by M. Stanley Livingston and
Edwin M. McMillan in physics today,
October 1959, 18-34, and Livingston’s
Particle Accelerators: A Brief History
(Harvard, Cambridge, 1969).

25. D. Cooksey to M. S. Livingston, 8 June

1938, E. O. Lawrence Papers, Bancroft
Library, University of California, Berk-
eley. □

340

HISTORY OF PHYSICS

The idea of the neutrino

To avoid anomalies of spin and statistics Pauli suggested in 1930
that a neutral particle of small mass might accompany the electron in nuclear
beta decay, calling it (until Chadwick’s discovery) the neutron.

Laurie M. Brown physics today / September 1978

During the 1920’s physicists came to ac-
cept the view that matter is built of only
two kinds of elementary particles, elec-
trons and protons, which they often
called1 “negative and positive electrons.”
A neutral atom of mass number A and
atomic number Z was supposed to contain
A protons, all in the nucleus, and A neg-
ative electrons, A — Z in the nucleus and
the rest making up the external electron
shells of the atom. Their belief that both
protons and negative electrons were to be
found in the nucleus arose from the ob-
servations that protons could be knocked
out of light elements by alpha-particle
bombardment, while electrons emerged
spontaneously (mostly from very heavy
nuclei) in radioactive beta decay. Any
other elementary constituent of the atom
would have been considered superfluous,
and to imagine that another might exist
was abhorrent to the prevailing natural
philosophy.

Nevertheless, in December 1930
Wolfgang Pauli suggested a new elemen-
tary particle that he called a neutron,
with characteristics partly like that of the
nucleon we now call by that name, and
partly those of the lepton that we now call
neutrino (more precisely the electron
antineutrino, but this distinction is not
needed here). Pauli’s neutron-neutrino
idea became well-known to physicists
even before his first publication of it,
which is in the discussion section fol-
lowing Heisenberg’s report on nuclear
structure at the Seventh Solvay Confer-
ence,2 held in Brussels in October 1933.

Shortly after attending this conference,
Enrico Fermi published his theory of beta
decay, which assumes that a neutrino al-
ways accompanies the beta-decay elec-

Laurie M. Brown is a professor in the Department
of Physics and Astronomy, Northwestern Uni-
versity, Evanston, Illinois.

tron, and that both are created at their
moment of emission. Perhaps because of
the rapid acceptance of Fermi’s theory
and the tendency to rethink history “as it
should have happened,” the true nature
of Pauli’s proposal has been partly over-
looked and its radical character insuffi-
ciently emphasized. Contrary to the
impression given by most accounts, Pau-
li’s “neutron” has some properties in
common with the neutron James Chad-
wick discovered in 1932 as well as with
Fermi’s neutrino.

Flaws in the model

By the end of 1930, when our story be-
gins, quantum mechanics had triumphed
not only in atomic, molecular and crystal
physics, but also in its treatment of some
nuclear processes, such as alpha-particle
radioactivity and scattering of alpha
particles from nuclei (including the case
of helium, in which quantum-mechanical
interference effects are so important).
However, the situation regarding elec-
trons in the nucleus was felt to be critical.
The main difficulties of the electron-
proton model of the nucleus were:

► The symmetry character of the nuclear
wave function depends upon A, not Z as
predicted by the model; when A - Z is
odd the spin and statistics of the nucleus
are given incorrectly. For example, ni-
trogen (Z = 7, A = 14) was known from
the molecular band spectrum of N2 to
have spin 1 and Bose-Einstein statis-
tics.

► No potential well is deep enough and
narrow enough to confine a particle as
light as an electron to a region the size of
the nucleus (the argument for this is
based on the uncertainty principle and
relativistic electron theory).

► It is hard to see how to “suppress” the
very large (on the nuclear scale) magnetic
moments of the electrons in the nucleus,

which conflict with data on the hyperfine
structure of atomic spectra.

► Although both alpha and gamma decay
show the existence of narrow nuclear en-
ergy levels, the electrons from a given
beta-decay transition emerge with a broad
continuous spectrum of energy.

The strong contrast between the suc-
cesses and the failures of quantum me-
chanics applied to the nucleus are no-
where more evident than in a book by
George Gamow.3 In it, all the passages
concerning electrons in the nucleus are set
off in warning symbols (skull and cross-
bones in the original manuscript).

Some physicists (among them Niels
Bohr and Werner Heisenberg4) took these
difficulties to indicate that a new dy-
namics, possibly even a new type of
space-time description, might be appro-
priate on the scale of nuclear distances
and energies, just as quantum mechanics
begins to be important on the atomic
scale. These physicists were impressed
by the similarity of the nuclear radius to
the value e2/mc2, the classical electron
radius of H. A. Lorentz. At this distance
it had been anticipated that electrody-
namics would probably fail (and maybe,
with it, the special theory of relativity).
Bohr was willing to relinquish the con-
servation of energy, except as a statistical
law, in parallel with the second law of
thermodynamics. At the same time
Heisenberg was considering the intro-
duction of a new fundamental length into
the theory. It seemed that anything
might be considered acceptable as a way
out of the dilemma — or perhaps anything
except a new elementary particle.

Pauli’s proposal

It was in this context of ideas that Pauli
dared to suggest the existence of a new
neutral particle. His proposal, intended
to rescue the quantum theory of the nu-

PARTICLES AND QUANTA

341

GOUDSMIT COLLECTION, AIP NIELS BOHR LIBRARY

PAULI ON THE WAY TO PASADENA, 1931

cleus from its contradictions, was pre-
sented in good humor as a “desperate
remedy,” although it was a serious one.
(The Viennese version would have been,
according to the old joke: desperate, but
not serious.) During the next three years
he lectured on what he called the “neu-
tron” at several physics meetings and he
discussed it privately with colleagues.

Pauli’s first proposal was put forward
only tentatively, as he recalled in a lecture
he delivered in Zurich in 1957, after re-
ceiving news of the experiments con-
firming parity violation in beta decay.5
Invited to a physics meeting in Tubingen,
Germany, which he was unable to attend
(because of a ball to be held in Zurich, at
which he declared he was “indispens-
able”), he sent a message with a colleague
as an “open letter,” although it was in-
tended mainly for Hans Geiger and Lise
Meitner. An English translation of this
letter is given in the Box on page 27.
Pauli was anxious for their expert advice
as to whether his proposal was compatible
with the known facts of beta decay.

In the 1957 lecture Pauli also tells how
he became convinced of a crisis associated
with beta decay. During the decade that
followed the discovery by Chadwick in
1914 of beta rays with a continuous energy
spectrum, it became established that
these were the true “disintegration elec-
trons,” rather than those making up dis-
crete electron line spectra, which were
later shown to arise from such causes as
photoelectric effects of nuclear gamma
rays, internal conversion and Auger pro-
cesses. Because a continuous spectrum
seemed to disagree with the presence of

discrete quantum states of the nucleus (as
indicated by alpha and gamma emission),
some workers, including Meitner, thought
that the beta rays were radiating some of
their energy as they emerged through the
strong electric field of the nucleus.5’6’7

This led C. D. Ellis and William
Wooster at the Cavendish Laboratory in
Cambridge, England, who did not believe
in the radiation theory, to perform a ca-
lorimetric experiment with radium E
(bismuth) as a source. Their result, later
confirmed in an improved experiment by
Meitner and W. Orthmann,8 was that the
energy per beta decay absorbed in a
thick-walled calorimeter was equal to the
mean of the electron energy spectrum,
and not to its maximum (endpoint).
Furthermore, Meitner showed that no
gamma rays were involved. According to
Pauli (in 1957), this allowed but two pos-
sible theoretical interpretations:

► The conservation of energy is valid only
statistically for the interaction that gives
rise to beta radioactivity.

► The energy theorem holds strictly in
each individual primary process, but at
the same time there is emitted with the
electron another very penetrating radia-
tion, consisting of new neutral particles.
To the above, Pauli adds, “The first pos-
sibility was advocated by Bohr, the second
by me.” 5

But although the conservation of en-
ergy, and possibly other conservation laws
in beta decay were very much in Pauli’s
mind at this time, this was not his only
reason for proposing the neutrino. He
makes this point (already obvious from
his Tubingen letter) quite explicit in his

1957 Zurich lecture. After pointing out
one of the major difficulties with the nu-
clear model containing only protons and
electrons (the symmetry argument men-
tioned above), Pauli says:

“I tried to connect this problem of the
spin and statistics of the nucleus with the
other of the continuous beta spectrum,
without giving up the energy theorem,
through the idea of a new neutral parti-
cle.”

Neutrinos — ejected or created?

It is often overlooked in discussing the
history of the neutrino idea that Pauli
suggested his particle as a constituent of
the nucleus, with a small but not zero
mass, together with the protons and the
electrons. (Chien-Shiung Wu, for ex-
ample, emphasizes the non-conservation
of statistics that would occur in beta decay
without the neutrino.6’7’9 However, Pauli
refers rather to the spin and statistics of
stable nuclei such as lithium 6 and nitro-
gen 14.) This point is of some signifi-
cance; had Pauli proposed in 1930 that
neutrinos were created (like photons) in
transitions between nuclear states, and
that they were otherwise not present in
the nucleus, he would have anticipated by
three years an important feature of Fer-
mi’s theory of beta decay. Pauli did not
claim to have had this idea when he wrote
the Tubingen letter, but he did say (in his
Zurich lecture) that by the time he was
ready to speak openly of his new particle,
at a meeting of The American Physical
Society in Pasadena, held in June of 1931,
he no longer considered his neutrons to be
nuclear constituents. It is for this reason,
he says, that he no longer referred to them
as “neutrons”; indeed, that he made use
of no special name for them. However,
there is evidence, as we shall see, that
Pauli’s recollections are incorrect; that at
Pasadena the particles were called neu-
trons and were regarded as constituents
of the nucleus.

I have not been able to obtain a copy of
Pauli’s Pasadena talk or scientific notes
on it; he said later that he was unsure of
the matter and thus did not allow his
lecture to be printed. The press, how-
ever, took notice. For example, a short
note in Time, 29 June 1931, headed
“Neutrons?”, says that Pauli wants to add
a fourth to the “three unresolvable basic
units of the universe” (proton, electron
and photon); adding, “He calls it the
neutron.”

Upon examining the program of the
Pasadena Meeting, I discovered that
Samuel Goudsmit spoke at the same ses-
sion as Pauli (and even upon the same
announced subject — hyperfine structure).
I wrote to Goudsmit and received a most
interesting reply, from which I should like
to quote:

“Pauli accompanied my former wife

and me on the train trip across the

US. I forgot whether we started in

Ann Arbor or arranged to meet in Chi-

342

HISTORY OF PHYSICS

GOUDSMIT COLLECTION, AIP NIELS BOHR LIBRARY

GOUDSMIT (MIDDLE) AND FERMI (RIGHT) WITH UNIDENTIFIED MAN

cago. We talked little physics, more
about physicists. Pauli’s main topic
at the time was that he could imitate
P. S. Epstein and he insisted that I
take pictures of him while doing that.
We spent a couple of days in San
Francisco, where we almost lost him in
Chinatown. He’d suddenly rush
ahead and around a corner while we
were window shopping ... He may
have talked about the “neutron” on
that trip, but I am not at all certain

Goudsmit does not now recall exactly
what Pauli said at Pasadena, except that
he mentioned the “neutron”; however, he
sent me a copy of his report at the Rome
Congress on what Pauli had said four
months earlier in Pasadena. To continue,
then, with Goudsmit’s letter:

“Fermi was arranging what was prob-
ably the first nuclear physics meeting.
It was held in Rome in October 1931
... It was the best organized meeting I
ever attended, because there was very
much time available for informal dis-
cussions and get-togethers . . . Fermi
had arranged marvelous leisurely
sightseeing trips for the group. There
were about 40 guests and 10 Italians.

“Fermi ordered the then ‘young’
participants, namely [Nevill] Mott,
[Bruno] Rossi, [George] Gamow (who
could not leave Russia but sent a man-
uscript) and myself, to prepare sum-
mary papers for discussion ... As you
know, I don’t use and don’t keep
notes. But I have a clear picture of
Pauli lecturing [at Pasadena] and his
mention of the ‘neutron’ . . . Pauli was
supposed to attend the Rome meet-
ing, but he arrived a day or so late. In
fact, he entered the lecture hall the
very moment that I mentioned his
name! Like magic! I remarked
about it and got a big laugh from the
audience.”

Goudsmit’s Rome report

At Fermi’s request, then, Goudsmit
reported at the Rome Conference on
Pauli’s talk in Pasadena. Here is what he
said:10

“At a meeting in Pasadena in June
1931, Pauli expressed the idea that
there might exist a third type of ele-
mentary particles besides protons and
electrons, namely ‘neutrons.’ These
neutrons should have an angular mo-
mentum V2 h/2ir and also a magnetic
moment, but no charge. They are
kept in the nucleus by magnetic forces
and are emitted together with beta-
rays in radioactive disintegration.
This, according to Pauli, might re-
move present difficulties in nuclear
structure and at the same time in the
explanation of the beta-ray spectrum,
in which it seems that the law of con-
servation of energy is not fulfilled. If
one would find experimentally that
there is also no conservation of mo-

mentum, it would make it very proba-
ble that another particle is emitted at
the same time with the beta-particle.
The mass of these neutrons has to be
very much smaller than that of the
proton, otherwise one would have de-
tected the change in atomic weight
after beta-emission.”

Goudsmit added that Pauli believed
“neutrons may throw some light on the
nature of cosmic rays.”

It does appear clear from this passage
(to which Pauli evidently made no objec-
tion at the time) that at Pasadena the
neutron was intended to be a particle that
could be bound in the nucleus by mag-
netic forces. In his letter to me Goudsmit
also said, “It was Maurice Goldhaber who
some time ago pointed out that I was the
first to put Pauli’s idea on paper and in
print.”

After leaving Pasadena Pauli remained
in the United States until the fall, when
he went to Rome. He gave a seminar at
the Summer Session of the University of
Michigan at Ann Arbor (probably at one
of their Symposia on Theoretical Physics,
where Fermi had, the previous summer,
given his famous lectures on the quantum
theory of radiation). At the seminar
Pauli spoke, according to the Berkeley
theorists J. F. Carlson and J. Robert Op-
penheimer,11 about “the elements of the
theory of the neutron, its functions and its
properties.”

Tracks in the cloud chamber

Carlson and Oppenheimer wondered
whether Pauli’s “neutrons” could be used
to solve yet another puzzle: the appear-

ance of certain lightly ionizing cloud-
chamber tracks from cosmic rays that had
been reported.

The complex problem of the energy loss
of relativistic charged particles was crucial
to the interpretation of the various com-
ponents of the cosmic rays observed in the
atmosphere, and had attracted the at-
tention of many theorists. Carlson and
Oppenheimer were unable to account for
cloud-chamber tracks that appeared
thinner than those of an “ordinary ra-
dioactive” beta particle. Their calcula-
tions of energy loss (which agreed in a
general way with independent calcula-
tions by Heisenberg and Hans Bethe, and
with an older classical estimate by Bohr)
showed that charged particles should have
a relativistic increase of ionization with
energy. The particles leaving light tracks
were very penetrating (and thus probably
relativistic) and it was concluded that
they could not be electrons or protons.
(These quarklike tracks have not, to my
knowledge, been explained. Perhaps
they were examples of old and “faded”
tracks, which often plagued cloud cham-
bers of the untriggered variety.)

Carlson and Oppenheimer decided
therefore to make a theoretical investi-
gation, as they said,11 of the “ionizing
power of the neutrons which were sug-
gested by Pauli to salvage the theory of
the nucleus. These neutrons, it will be
remembered, are particles of finite proper
mass, carrying no charge, but having a
small magnetic moment . . .”

Could thin tracks, like those in the
cosmic rays, be seen from beta decays?

“If they were found, we should be cer-

PARTICLES AND QUANTA

343

AIP NIELS BOHR LIBRARY

The participants in the Seventh Solvay Conference, where Pauli pre-
sented his neutrino idea, included, in the first row, E. Schrodinger, I. Joliot,
N. Bohr, A. Joffe, M. Curie, O. W. Richardson, P. Langevin. Lord Ruther-
ford, T. De Donder, M. de Broglie, L. de Broglie, L. Meitner, J. Chadwick,
and in the second row, E. Henriot, F. Perrin, F. Joliot, W. Heisenberg, H.

A. Kramers, E. Stahel, E. Fermi, E. T. S. Walton, P. A. M. Dirac, P, Debye,
N. F. Mott, B. Cabrera, G. Gamow, W. Bothe, P. M. S. Blackett, M. S.
Rosenblum, J. Errera, E. Bauer, W. Pauli, J. E, Verschaffelt, M. Cosyns
(in back), E. Herzen, J. D. Cockcroft, C. D, Ellis, R. Peierls, A. Piccard,
E. 0. Lawrence, L. Rosenfeld. The photograph is by Benjamin Couprie.

tain that the neutrons not only played
a part in the building of nuclei, but
that they also formed the cosmic
rays.”

The calculations of Carlson and Op-
penheimer were published12 almost a year
later, in September 1932; by that time
they no longer believed that “neutrons”
might leave observable cloud-chamber
tracks. In addition, the situation in nu-
clear physics had changed profoundly, as
it also was about to in cosmic-ray physics:
Chadwick’s study of “the penetrating
radiation produced in the artificial dis-
integration of beryllium” had revealed the
existence of the neutron, announced the
previous February; Anderson’s discovery
of the positron in cosmic rays was an-
nounced in August.13 Certainly one
could no longer speak of the proton as
synonymous with positive electricity, and
one might suppose that now a new parti-
cle like Pauli’s would be acceptable; but
this was not the case:

For one thing, the positron was thought
to be only the absence of a negative elec-
tron of negative energy, a hole in the
vacuum. For another, the neutron of
Chadwick, the heavy neutron, was gen-
erally regarded as a composite object (it
was not thought to be unstable when free),
a kind of tightly bound hydrogen atom or
neutral nucleus made of a proton and an
electron, like other nuclei. It was perhaps
thought to be elementary only by Ettore
Majorana in Rome who (according to
Emilio Segre) called it the neutral pro-
ton.

For our purposes, the Carlson-Op-
penheimer article is significant in what it
tells us about the view held by Pauli, in
that summer of 1931, about his neutral
particle, which, following the Berkeley
authors, we will now call the magnetic

neutron to distinguish it from Chadwick’s
neutron and Fermi’s neutrino. Carlson
and Oppenheimer state that the neutral
particle of spin V2, satisfying the exclusion
principle, was introduced by Pauli not
only to resolve the difficulties in nuclear
theory, but “on the further ground that
such a particle could be described by a
wave function which satisfies all the re-
quirements of quantum mechanics and
relativity . . . The experimental evidence
on the penetrating beryllium radiation
suggests that neutrons of nearly protonic
mass do exist; and since our calculations
may be carried through without specify-
ing the mass or magnetic moment of the
neutron, we shall consider the most gen-
eral particle which satisfies the wave
equation proposed by Pauli. It is im-
portant to observe that there may very
well be other types of neutral particles,
which are not elementary, and to which
our calculations do not apply . . .”

Thus we find, surprisingly, that there
were thought to be also purely theoretical
grounds for considering a neutral particle
with a magnetic moment; it is one of the
few simple types of elementary particles
that are allowed by relativistic quantum
theory. In the wake of Chadwick’s neu-
tron discovery, Carlson and Oppenheimer
in 1932 redefined Pauli’s particle to be one
whose wave function obeys a certain rel-
ativistic wave equation. We should not,
however, assume that the Berkeley theo-
rists were soft on new particles. On the
contrary, the final paragraph of their
lengthy article reads, “We believe that
these computations show that there is no
experimental evidence for the existence
of a particle like the magnetic neutron.”

Pauli’s wave equation for the neutral
particle, given at Ann Arbor, is a variant
of the linear Dirac equation for the elec-

tron, containing an additional term (Zu-
satzglied) called the “Pauli anomalous
magnetic moment” term.14 This equa-
tion describes a spin-V2 particle that may
be either charged or neutral; the extra
term makes a contribution to the
charge-current four-vector, which need
not vanish for a neutral particle.

Fermi is positive

Carlson and Oppenheimer derived a
general formula for the collision cross
section of magnetic neutrons and exam-
ined the result for small velocities. (They
were well aware of the perils involved in
pushing this highly singular interaction to
excessive energies.) For the collision of
a neutron against a particle of equal mass,
they found a large probability, nearly in-
dependent of velocity and proportional to
the square of the magnetic moment. The
average energy loss per collision was rel-
atively large, and they deduced that such
a particle “will never produce ion traces
in a cloud chamber, since it tends to lose
an appreciable fraction of its energy, and
suffer an appreciable deflection at every
impact.” For targets much lighter or
heavier than the neutron, smaller energy
losses occur; cloud-chamber tracks might
result in this case, but the collision
probabilities are small unless the mag-
netic moment of the neutron is assumed
to be improbably large. The concluded
(correctly) that there is no evidence for
magnetic neutrons. (The heavy neutron,
with a magnetic moment only one thou-
sandth of a Bohr magneton, leaves no
tracks.) At the Seventh Solvay Confer-
ence in 1933, Pauli no longer felt the
magnetic neutron to be “well-founded.”

Let us return now to the Rome Con-
gress of 1931, which Pauli considered
important in the development of the

344

HISTORY OF PHYSICS

neutrino concept, for there he had the
opportunity to discuss it with Bohr and
especially with Fermi, with whom he had
a number of private conversations. While
Fermi’s attitude toward the neutrino was
very positive, Bohr was totally opposed to
it, preferring to think that within nuclear
distances the conservation laws were
breaking down.15

“From the empirical point of view,”
said Pauli, “it appeared to me decisive
whether the beta spectrum of the elec-
trons showed a sharp upper limit” or, in-
stead, an infinitely falling statistical dis-
tribution. Pauli felt that if the limit were
sharp, then his idea was correct, and
Bohr’s was wrong.

In mid- 1933, Ellis and Mott suggested
that the beta-ray spectrum has indeed a
sharp upper limit, corresponding to a
unique energy difference between parent
and daughter nucleus.16 Furthermore,
they added,

“According to our assumption the /3-
particle may be expelled with less en-
ergy than the difference of the ener-
gies ... of the two nuclei, but not with
more energy. We do not wish in this
paper to dwell on what happens to the
excess energy in those disintegrations
in which the electron is emitted with
less than the maximum energy. We
may, however, point out that if the en-
ergy merely disappears, implying a
breakdown of the principle of energy
conservation, then in a /3-ray decay
energy is not even statistically con-
served. Our hypothesis is, of course,
also consistent with the suggestion of
Pauli that the excess energy is carried
off by particles of great penetrating
power such as neutrons of electronic
mass.”

The question of the upper limit of the
beta spectrum, although not easily re-
solved, is of some importance, for the
shape of the upper end of the spectrum is
sensitive to the neutrino mass. This was
discussed again by Ellis at an interna-
tional conference in London, held in the
fall of 1934, where he referred to accurate
magnetic spectrograph measurements of
W. J. Henderson that strongly suggested
a neutrino of zero mass.17 Fermi’s theory
of beta decay had already been pub-
lished,18 and Ellis assumed it in his anal-
ysis, but an energy-nonconserving theory,
that of Guido Beck and Kurt Sitte, shared
equal time with Fermi’s at the confer-
ence.

Fermi spoke at the London Conference,
but his subject was the neutron-activation
work of the Rome experimental nuclear
physics group. He also had attended the
Seventh Solvay Conference, held in Oc-
tober, 1933, where he heard Pauli present
his first suggestion for publication of the
existence of a neutrino. The complete
Solvay remarks of Pauli are given in En-
glish translation in the Box on page 28; we
leave it to the reader to decide whether
Pauli still thought that the neutrino or the

Pauli proposes a particle

The letter in which Pauli proposed the neutrino, translated from the German of reference 5,
reads as follows:

Zurich, 4 December 1930
Gloriastr.

Physical Institute of the
Federal Institute of Technology (ETH)
Zurich

Dear radioactive ladies and gentlemen,

As the bearer of these lines, to whom I ask
you to listen graciously, will explain more
exactly, considering the “false” statistics of
N-14 and Li-6 nuclei, as well as the contin-
uous /3-spectrum, I have hit upon a desperate
remedy to save the “exchange theorem" *
of statistics and the energy theorem.
Namely [there is] the possibility that there
could exist in the nuclei electrically neutral
particles that I wish to call neutrons, which
have spin ’/2 and obey the exclusion princi-
ple, and additionally differ from light quanta
in that they do not travel with the velocity of
light: The mass of the neutron must be of
the same order of magnitude as the electron
mass and, in any case, not larger than 0.01
proton mass. — The continuous /3-spectrum
would then become understandable by the
assumption that in ( 8 decay a neutron is
emitted together with the electron, in such
a way that the sum of the energies of neutron
and electron is constant.

Now the next question is what forces act
upon the neutrons. The most likely model
for the neutron seems to me to be, on wave
mechanical grounds (more details are known
by the bearer of these lines), that the neutron

at rest is a magnetic dipole of a certain mo-
ment p. Experiment probably requires that
the ionizing effect of such a neutron should
not be larger than that of a 7 ray, and thus p
should probably not be larger than e.10-13
cm.

But I don’t feel secure enough to publish
anything about this idea, so I first turn con-
fidently to you, dear radioactives, with the
question as to the situation concerning ex-
perimental proof of such a neutron, if it has
something like about 10 times the pene-
trating capacity of a 7 ray.

I admit that my remedy may appear to
have a small a priori probability because
neutrons, if they exist, would probably have
long ago been seen. However, only those
who wager can win, and the seriousness of
the situation of the continuous /3-spectrum
can be made clear by the saying of my hon-
ored predecessor in office, Mr. Debye, who
told me a short while ago in Brussels, "One
does best not to think about that at all, like
the new taxes." Thus one should earnestly
discuss every way of salvation. — So, dear
radioactives, put it to the test and set it
right. — Unfortunately I cannot personally
appear in Tubingen, since I am indispensable
here on account of a ball taking place in
Zurich in the night from 6 to 7 of Decem-
ber.— With many greetings to you, also to
Mr. Back, your devoted servant,

W. Pauli

* In the 1957 lecture, Pauli explains, “This reads: exclusion principle (Fermi statistics)
and half-integer spin for an odd number of particles; Bose statistics and integer spin for an
even number of particles.”

CHADWICK

AIP NIELS BOHR

PARTICLES AND QUANTA

345

Pauli becomes bolder

The discussion comments in which Pauli presented the idea of the neutrino at the Seventh
Solvay Conference, ref. 2. The text is based on the translation from the French original
by Chien-Shiung Wu, ref. 9, with corrections by Laurie Brown noted in brackets.

The difficulty coming from the existence of
the continuous spectrum of the (3-rays con-
sists, as one knows, in that the mean life-
times of nuclei emitting these rays, as that
of the resulting radioactive bodies, possess
well-determined values. One concludes
necessarily from this that the state as well as
the energy and the mass, of the nucleus
which remains after the expulsion of the /3
particle, are also well-determined. I will not
persist in efforts by which one could try to
escape from this conclusion for I believe, in
agreement with Bohr, that one always
stumbles upon insurmountable difficulties in
explaining the experimental facts.

In this connection, two interpretations of
the experiment present themselves. The
interpretation supported by Bohr admits that
the laws of conservation of energy and mo-
mentum do not hold when one deals with a
nuclear process where light particles play an
essential part. This hypothesis does not
seem to me either satisfying or even plau-
sible. In the first place the electric charge
is conserved in the process, and I don’t see
why conservation of charge would be more
fundamental than conservation of energy and
momentum. Moreover, it is precisely the
energy relations which govern several
characteristic properties of beta spectra
(existence of an upper limit and relation with
gamma spectra, Heisenberg stability crite-
rion). If the conservation laws were not
valid, one would have to conclude from these
relations that a beta disintegration occurs
always with a loss of energy and never a
gain; this conclusion implies an irreversibility
of these processes with respect to time,
which doesn't seem to me at all accept-
able.

In June 1931, during a conference in
Pasadena, I proposed the following inter-
pretation: the conservation laws hold, the
emission of beta particles occurring together
with the emission of a very penetrating ra-

diation of neutral particles, which has not
been observed yet. The sum of the energies
of the beta particle and the neutral particle
(or the neutral particles, since one doesn’t
know whether there be one or many) emitted
by the nucleus in one process, will be equal
to the energy which corresponds to the upper
limit of the beta spectrum. It is obvious that
we assume not only energy conservation but
also the conservation of linear momentum,
of angular momentum and of the character-
istics of the statistics in all elementary pro-
cesses.

With, regard to the properties of these
neutral particles, we first learn from atomic
weights [of radioactive elements] that their
mass cannot be much larger than that of the
electron. In order to distinguish them from
the heavy neutrons, E. Fermi proposed the
name “neutrino.” It is possible that the
neutrino proper mass be equal to zero, so
that it would have to propagate with the ve-
locity of light, like photons. Nevertheless,
their penetrating power would be far greater
than that of photons with the same energy.
It seems to me admissible that neutrinos
possess a spin % and that they obey Fermi
statistics, in spite of the fact that experiments
do not provide us with any direct proof of this
hypothesis. We don’t know anything about
the interaction of neutrinos with other ma-
terial particles and with photons; the hy-
pothesis that they possess a magnetic mo-
ment, as I had proposed once (Dirac’s theory
induces us to predict the possibility of neutral
magnetic particles) doesn’t seem to me at all
well founded.

In this connection, the experimental study
of the momentum difference [read balance]
in beta disintegrations constitutes an ex-
tremely important problem; one can predict
that the difficulties will be quite insur-
mountable [read very great] because of the
smallness of the energy of the recoil nucle-
us.

electron were constituents of the nucleus.
(That a massless neutrino could be
created at the moment of its emission
with the electron was clearly proposed
that year19 by Francis Perrin, who also
attended the Seventh Solvay Conference.)
There was, in any case, no doubt that a
light or massless neutral particle of spin
V2 has to be emitted with the beta-decay
electron in order to save the conservation
laws, and that is surely the idea of neu-
trino!

Fermi’s theory of beta decay is in many
ways still the standard theory. Called by
Victor Weisskopf “the first example of
modern field theory,”20 it eventually
caused Bohr to withdraw21 his doubts
concerning “the strict validity of the
conservation laws.” A radical generali-
zation of quantum theory was not re-
quired, though new particles and new in-
teractions were. Within a few months of
Fermi’s theory, positron beta decay was
seen (the first example of artificial ra-
dioactivity); and beta decay was to be the
prototype of a larger class of weak inter-
actions.

The neutrino can be regarded as one of
the first (if not the first) of the new par-
ticles that made the new physics of the
1930’s, even though it took two more
decades to observe the first neutrino-
capture event. The weak interactions
have been notorious for their capacity to
flout the expectations of physicists with
regard to symmetries and conservation
laws. Although Bohr was too willing, in
his 1931 Faraday Lecture,15 “to renounce
the very idea of energy balance,” the
conclusion of that lecture is probably still
appropriate today: . . notwithstanding

all the recent progress, we must still be
prepared for new surprises.”

* * *

This work was supported in part by a grant
from the National Science Foundation. I
would like to express my sincere appreciation
to Arthur L. Norberg of The Bancroft Library,
University of California , Berkeley, and to
Judith Goodstein of the Robert A. Millikan
Memorial Library of the California Institute
of Technology. I am much obliged to Samuel
Goudsmit for his letter and for his kind per-
mission to quote from it.

References

1. R. A. Millikan, in Encyclopedia Britan-
nica, 14th edition, volume 8, page 340
(1929).

2. Rapports du Septieme Conseil de Phy-
sique Solvay, 1933, Gauthier-Villars, Paris
(1934), page 324. Pauli’s remarks are in
French.

3. G. Gamow, Constitution of Atomic Nuclei
and Radioactivity, Oxford U.P. (1931).

4. J. Bromberg, Hist. Stud. Phys. Sci. 3, 307
(1971).

5. W. Pauli, Aufsatze und Vortrage iiber
Physik und Erkenntnistheorie, Braun-
schweig (1961); Collected Scientific Pa-
pers, volume 2, Interscience (1964), page
1313.

6. C. S. Wu, S. A. Moszkowki, Beta Decay,
Interscience (1966).

7. C. S. Wu, in Trends in Atomic Physics (O.
R. Frisch et al, eds.), Interscience (1959),
page 45; C. S. Wu, in Five Decades of Weak
Interactions (N. P. Chang, ed.), New York
Acad. Sciences, New York (1977), page 37;
A. Pais, Rev. Mod. Phys. 49, 925 (1977).

8. C. D. Ellis, W. A. Wooster, Proc. Roy. Soc.
(London) A 117, 109 (1927); L. Meitner, W.
Orthmann, Zeit. f. Phys. 60, 413 (1930).

9. C. S. Wu, in Theoretical Physics in the
Twentieth Century (H. Fierz, V. F. Weis-
skopf, eds.), Interscience (1960), page
249.

10. S. A. Goudsmit, in Convegno di Fisica
Nucleare, Reale Accademia d’ Italia, Atti,
Rome (1932), page 41.

11. J. F. Carlson, J. R. Oppenheimer, Phys.
Rev. 38, 1737 (1931).

12. J. F. Carlson, J. R. Oppenheimer, Phys.
Rev. 41,763 (1932).

13. C. Weiner, PHYSICS TODAY, May 1972,
page 40.

14. W. Pauli, in Handbuch der Physik, Band
24/i (1933), page 233; ref. 12, page 778.

15. N. Bohr, in ref. 10, page 119; J. Chem. Soc.
(London), page 349 (1932).

16. C. D. Ellis, N. F. Mott, Proc. Roy. Soc.
(London), A 141,502 (1933).

17. C. D. Ellis, in International Conference on
Physics, London, 1934, Vol. I, Nuclear
Physics, Cambridge (1935); W. ■). Hen-
derson, Proc. Roy. Soc. (London) A 147,
572 (1934).

18. E. Fermi, Z. f. Phys. 88, 161 (1934); English
translation: F. L. Wilson, Amer. J. Phys.
36,1150(1968).

19. F. Perrin, Compt. Rend. 197,1625(1933).

20. V. F. Weisskopf, in Exploring the History
of Nuclear Physics (C. Weiner, ed.), Amer.
Inst, of Physics, N.Y. (1972), page 17.

21. N. Bohr, Nature 138, 25 (1936). □

The birth of
elementary-panicle

PHYSICS TODAY / APRIL 1982

In the 1930s and 1940s physicists significantly revised
their views on the elementary constituents
of matter, which during the 1920s they had assumed
to be only the electron and the proton.

Laurie M. Brown and
Lillian Hoddeson

By 1930, relativity and quantum me-
chanics were established, yet the exci-
tement of the new physics was far from
over. Indeed, the next half-century
was characterized by startling experi-
mental and theoretical discoveries and
by new puzzles that appeared wherever
one looked.

In the late 1920s all matter was
thought to be made up of protons and
electrons. There were, of course, many
difficulties with this view, and the ef-
fort to revise it led to new problems —
and to the birth of the field of modern
elementary-particle physics. Three
currents flowed together to make parti-
cle physics: nuclear physics, cosmic
rays and quantum field theory. By the
mid-1980s, there was conflict and ap-
parent paradox where these fields over-
lapped, and although some of the con-
flict was resolved by the end of the
1940s, the resolution raised new and
urgent problems.

Today there is increasing interest in
this historical process. An interna-
tional symposium was held recently at
Fermilab to study the history of parti-
cle physics through lectures by impor-
tant participants and through discus-
sions among physicists and historians.
An earlier symposium, at the Univer-
sity of Minnesota,1 considered the role
of nuclear physics in the origins of
particle physics. This article is an out-
growth of the Fermilab meeting, which
concentrated mainly on the parts
played by cosmic rays and quantum
field theory in the emergence of the

Laurie M. Brown is professor of physics and
astronomy at Northwestern University in Ev-
anston, Illinois. Lillian Hoddeson is historian of
physics at Fermilab and in the physics depart-
ment of the University of Illinois at Urbana-
Champaign.

new field. In the discussion of the
origins of particle physics with which
we begin this article, we retain that
emphasis: We will mention the role of
the atomic nucleus, but we shall con-
centrate on the roles of cosmic rays and
theory.

The nucleus and cosmic rays

There were many problems in treat-
ing the nucleus as a quantum mechani-
cal system of protons and electrons.

► The nucleus was supposed to contain
A protons and A — Z electrons. But
when the latter number is odd, as for
lithium-6 or nitrogen-14, the spin and
statistics are incorrect.

► Moreover, unpaired electron spins
in the nucleus implied a hyperfine
splitting of atomic spectral lines on a
scale about a thousand-fold larger than
is observed.

► In the relativistic quantum theory of
the electron it was impossible to con-
fine the light electron within the small
nucleus.

► Finally, there was the continuous
spectrum of /?-decay electron energies,
which called into question even the
conservation of energy.

Physicists seriously considered radi-
cal suggestions for modifying the me-
chanics, the electrodynamics and even
the conservation laws. But the resolu-
tion was to hinge on new particles: the
neutron, discovered by James Chad-
wick in 1932, and the neutrino, pro-
posed by Wolfgang Pauli in 1930 and
incorporated in a theory of /? decay by
Enrico Fermi in 1934. These two neu-
tral particles permitted the banish-
ment of electrons from nuclear models.
Soon after Carl David Anderson’s 1932
discovery of the positron in cosmic rays,
Irene Curie and Frederic Joliot pro-
duced artifically radioactive light ele-
ments that decayed by positron emis-
sion, and the picture of nuclear P decay
was complete.

Cosmic rays were discovered as a
result of post-1900 investigations of

fine-weather “atmospheric electricity,”
that is, ionization in the absence of an
electrical thunderstorm. After one had
accounted for all known sources of
ionization, there remained a “residual”
conductivity, even in closed vessels that
were heavily shielded. This pheno-
menon implied the existence of a pene-
trating radiation of unknown origin.

Researchers — notably Victor F. Hess
in Austria — conducted balloon flights,
mainly in central Europe, to investi-
gate altitude dependence of atmospher-
ic conductivity. The manned balloons
carried sealed electrometers whose
rates of discharge first decreased with
altitude, but then (above 2 km) began a
marked increase. This pattern of ioni-
zation suggested the existence of an
extraterrestrial source for the pene-
trating radiation, so that by the late
1920s one spoke of the cosmic rays (see
box on page 39, Discovery). Until 1930,
their specific ionization (ions per cm3
per sec) was the only property system-
atically observed.

The focus changed at the end of the
1920s when researchers used two meth-
ods, coincidence counting and the cloud

Carl Anderson and control panel for cloud
chamber in trailer on Pike's Peak, 1935.
(Courtesy of Carl Anderson.)

chamber with magnetic field, to study
the individual behavior of the charged
particles produced by collisions of pri-
mary cosmic rays with air molecules.
They adapted both methods from tech-
niques used to study x rays and radioac-
tivity. The two methods were flexible,
permitting a variety of experiments to
be performed; and they could be com-
bined. Their descendants are the prin-
cipal tools used today to study the
interactions of elementary particles,
whether the source be cosmic rays or
accelerators. The pioneers in this en-
terprise were Walter Bothe and
Werner Kolhorster in Berlin and
Dmitry Skobeltzyn in Leningrad.

Improved detectors. Kolhorster, a col-
league of Bothe at the Physikalisch-
Technische Reichsanstalt in Charlot-
tenburg, outside Berlin, and an exper-
ienced cosmic-ray worker, pointed out
in 1928 that by aligning two point-
counters in a vertical array, one could
use Bothe’s counting technique of coin-
cidence to make a y-ray telescope for
cosmic rays. Bothe and Kolhorster
then implemented a similar scheme,
using the far-more-efficient Geiger-

Miiller tube counter. By mid-1929 they
established that a 4.1-cm-thick gold
block placed between the counters re-
duced the coincidence rate by only
24%, and they concluded from this that
the primary rays had a “corpuscular
nature.”2 Until then the rays had been
thought to be high-energy photons and
had been called (by Hess, for example)
“ultra y rays.”

Bruno Rossi, at the physics labora-
tory of the University of Florence in
Arcetri, Italy, soon found a way to
improve the technique. By using a
vacuum-tube circuit to detect the coin-
cident discharges of the tube counters,
he achieved greater flexibility and time
resolution. With three out-of-line
counters, he discovered that there was
a great abundance of secondary radi-
ation— later identified as “cascade
showers.”

Meanwhile in Leningrad, Skobelt-
zyn, who had been studying y radiation
from radioactive materials, began us-
ing the Wilson cloud chamber to ob-
serve the trajectories of cosmic-ray par-
ticles in a magnetic field. In such a
field a charged particle’s track is

curved, with a radius of curvature di-
rectly proportional to the particle’s mo-
mentum and inversely proportional to
the magnetic field. Skobeltzyn noted
that the tracks appeared to be associat-
ed with each other, to a degree difficult
to account for by the scattering pro-
cesses known at that time.3 His was
the first method for studying the inter-
actions of particles of energies higher
than those available from radioactive
sources.

Skobeltzyn’s counterpart in Califor-
nia was Carl David Anderson, who had
been using a cloud chamber to study
photoelectrons produced by x rays. An-
derson wanted to move on to study
Compton collisions of nuclear y rays,
but in 1930, at the urging of his boss,
Robert A. Millikan, he began tooling up
a cloud chamber and a strong magnetic
field to observe cosmic-ray interactions.
Anderson was to discover two new par-
ticles in cosmic rays: the positron and
the muon.4

The other major step forward was
Patrick M. S. Blackett and Giuseppe P.
S. Occhialini’s invention and use in
1932 of the counter-controlled cloud
chamber.6 In such a chamber, both the
expansion and camera are activated by
an electronic pulse from a counter ar-
ray that selects a class of events, so that
the incident particle “takes its own
picture.” Soon after Anderson had dis-
covered what he referred to as “easily
deflectable positives,” Blackett and Oc-
chialini used their new instrument to
observe electron pair production and
cascade showers. By 1930, therefore,
the technical framework had been es-
tablished for two decades of spectacular
cosmic-ray and new-particle discover-
ies, made using counter and cloud-
chamber techniques.

Theory

Relativistic electron theory, which
led to the “prediction” of the positron,
and the quantum theory of fields were
both on the agenda of theoretical phy-
sics after Werner Heisenberg and Er-
win Schrodinger invented quantum
mechanics in 1925 and 1926. Both
theories emerged from the fertile brain
of Paul A. M. Dirac. In a pioneering
work of February 1927 on quantum
electrodynamics (QED), Dirac proposed
a solution to the problem of the wave-
particle duality, which had puzzled
physicists since Albert Einstein hy-
pothesized the light-quantum in 1905.®
At the end of his paper, Dirac summar-
ized its contents as follows:

The problem is treated of an as-
sembly of similar systems satisfy-
ing the Einstein-Bose statistical

348

HISTORY OF PHYSICS

mechanics, which interact with an-
other different system, a Hamil-
tonian function being obtained to
describe the motion. The theory is
applied to the interaction of an
assembly of light-quanta with an
ordinary atom, and it is shown that
it gives Einstein’s laws for the
emission and absorption of radi-
ation.

The interaction of an atom with
electromagnetic waves is then con-
sidered, and it is shown that if one
takes the energies and phases of
the waves to be q-numbers satisfy-
ing the proper quantum conditions
instead of c-numbers, the Hamil-
tonian function takes the same
form as in the light-quantum treat-
ment. The theory leads to the
correct expressions for Einstein’s
j4s and 5s.

(The ^4s and 5s are light-quantum emis-
sion and absorption probability ampli-
tudes.) From this we can see that Dirac
treated the electromagnetic field as a
Bose-Einstein gas of light-quanta. The
following year, Pascual Jordan and Eu-
gene Wigner gave the analogous treat-
ment for a Fermi-Dirac gas, applicable
to electrons.7 The Jordan-Wigner type
of quantization, designed to prohibit
more than one electron from occupying
a given state, was just what Dirac
needed to formulate the theory of holes
and the notion of antimatter.

In his 1927 papers on the quantum
theory of the electromagnetic field,
Dirac quantized only the radiation part
of the field, consisting of transverse
waves. The Coulomb interaction was
considered a part of the energy of the
“matter” system, that is, the charged
particles. This separation is conven-

ient and often is a calculational necessi-
ty. However, as Gregor Wentzel has
remarked, it “not only appears con-
trary to the spirit of Maxwell’s theory,
but also raises questions from the view-
point of relativity theory. . . the split-
ting is not [relativistically] invariant.”8
Thus, in 1929, Heisenberg and Pauli
took up a task whose completion would
require the best theoretical efforts of
the next two decades:

... to connect, in a contradiction-
free manner, mechanical and elec-
trodynamic quantities, electro-
magneto-static interaction, on the
one hand, and radiation-induced
interactions on the other, and to
treat them from a unified view-
point. Especially [to take] into
account in a correct manner the
finite propagation velocity of elec-
tromagnetic forces.9
In the course of this work they disco-
vered that the self-mass of the point
electron was infinite, just as in the
classical theory. (See box on page 42.)
It was not until the postwar period that
a more self-consistent QED was
achieved. Nevertheless, the admitted-
ly imperfect QED could still be fa-
shioned into an effective tool for ana-
lyzing the high-energy cosmic rays.

QED and cosmic rays

Some disturbing experiments at
moderate energies — energies some-

Paul A. M. Dirac (at right) in Ann Arbor,
Michigan, in 1929. Leon Brillouin is in the
background.

Robert A. Millikan and G. Harvey Cameron

(below) with early cosmic-ray electroscopes.
In this photo, taken about 1925, Millikan (left)
is holding some lead shielding and Cameron
an electroscope. (Photos courtesy AIP Niels

Bohr Library.)

what larger than twice the rest mass
energy of the electron — showed a
much greater energy degradation
and scattering of high-energy y rays
than was predicted by a Compton-
effect calculation based on Dirac’s
relativistic electron theory.10 By
1933, the excess absorption was
found to be due to the production of
electron-positron pairs, and the ex-
cess “scattering” was traced to pho-
tons produced by pair annihilation.
This resolved the “doubts at 2 me2,”

PARTICLES AND QUANTA

349

which, however, moved then to 137me2.

The existence of doubts about the
validity of QED at energies of the order
of 137 me2 is corroborated by Anderson,
who says that in 1934 members of the
Caltech group spoke among themselves
of “ ‘green’ electrons and ‘red’ elec-
trons— the green electrons being the
penetrating type, and the red the
absorbable type.” But the green elec-
trons did not behave like electrons.
Although the formulas giving the ioniz-
ation energy loss for very fast charged
particles were considered to be accu-
rate, there seemed to be a problem with
the radiation formulas, even in 1934.
Referring to Anderson’s analysis of
cloud chamber photographs, Hans
Bethe and Walter Heitler said that
“the theoretical energy loss by radiation
is far too large to be in any way reconcil-
able with the experiments of Ander-
son.”u For the particles of energy 300
MeV (the assumed green electrons),
Anderson found an energy loss of 35
MeV per centimeter of lead, whereas
Bethe and Heitler concluded that “it
seems impossible that the theoretical
energy loss can be smaller than about
150 million volts per centimetre lead
for Anderson’s electrons.”

Instead of suggesting that these
strangely behaving electrons might be
some other particles, Bethe and Heitler
proposed a possible explanation that
reveals the spirit of the time:

This can perhaps be understood for
electrons of so high an energy. The
de Broglie wave-length of an elec-
tron having an energy greater than
137mc2 is smaller than the classi-
cal radius of the electron
r0 = e2/mc2. One should not expect
that ordinary quantum mechanics
which treats the electron as a
point-charge could hold under
these conditions. It is very inter-
esting that the energy loss of the
fast electrons really proves this
view and thus provides the first
instance in which quantum me-
chanics apparently breaks down for
a phenomenon outside the nucleus.
We believe that the radiation of
fast electrons will be one of the most
direct tests for any quantum-elec-
trodynamics to be constructed ,n
QED proves indispensable. The prob-
lem was not with QED but with the
assumption that Anderson’s penetrat-
ing high-energy “green” electrons were
electrons. They were, in fact, meso-
trons (now called muons), about 200
times as massive. But about three
years had to pass before anyone had the
courage, or the faith in QED, to ascribe
the discrepancy to new particles.

It was tempting at the time to ex-
plain away discrepancies between ob-
served high-energy phenomena and
theoretical expectations by appealing
to a breakdown of QED at small dis-

tances, at a “fundamental length” or at
the corresponding large momenta. But
this became impossible by 1937; by that
time, through a complex series of steps,
QED showed itself to be not only useful
after all, in spite of its menacing infini-
ties, but also the indispensable means
for understanding the nature of the
cosmic rays. Although the electrody-
namics of such energetic particles were
questioned, Evans James Williams
showed in 1933 that the important
momentum transfers involved are
small and that in a suitably chosen
reference frame the collisions are gen-
tle ones that do not involve high ener-
gies or small distances.12

In another step, taken in 1934, Bethe
and Heitler calculated the relativistic
formulas for bremsstrahlung (x-ray
production) and electron pair creation.
As noted earlier, they found significant
disagreement with Anderson’s results
when they assumed Anderson was
looking at electrons. Also, Williams
and Carl-Friedrich von Weizsacker
showed that no disagreement with the-
ory was to be expected, even if QED
were to break down at 137 me2. Again,
the argument was based upon looking
at the collisions in a suitable rest
frame.12 As Williams said in his 1935
article, “We find that the quantum
mechanics which enter into the exist-
ing treatments really concerns ener-
gies of the order of me 2 however big the
energy of the electron or photon.”

By 1937 QED had also demonstrated
its usefulness by explaining the behav-
ior of the “soft component” of the
cosmic rays, the cascade showers.
Many physicists contributed to the so-
lution of this problem; the first suc-
cesses were by Homi J. Bhabha and
Heitler, and by J. F. Carlson and J.
Robert Oppenheimer.13 However, the
infinities of QED remained, and to
obtain useful results they had to be
ignored or thought of as corrections
that would be “small,” were they calcu-
lable in finite terms.

Particles envisioned, particles seen

The particle discoveries of the early
1930s (if we can call the neutrino pro-
posal a discovery) permitted the ban-
ishment of electrons from the nucleus.
On the heels of the discovery of the
neutron, Heisenberg made a model of
the nucleus as a non-relativistic quan-
tum-mechanical system of neutrons
and protons in which the neutron was
to some extent treated as an elemen-
tary particle, the neutral counterpart
of the proton. However, within this
scheme Heisenberg tried to model the
neutron as a tightly bound compound
of proton and electron, in which the
electron loses most of its properties —
notably its spin, magnetic moment, and
fermion character. The dominant nu-
clear force was to consist of the ex-

Development of cosmic-ray
physics

In successive periods there was always
at least one change that was so significant
that it required a totally new interpretation
of the previous observations.

Prehistory (to 1911, especially from
1900):

► “Atmospheric electricity" during calm
weather

► Conductivity of air measured by
electrometers

► Connection with radioactivity of earth
and atmosphere

► Geophysical and meteorological
interest

Discovery (1911-1914) and
exploration (1922-1930):

► Observers with electrometers ascend in
balloons and measure the altitude depen-
dence of ionization, showing that there is
an ionizing radiation that comes from
above

► Such measurements begin in 1 909 and
continue (at interval) to about 1930, in the
atmosphere, under water, underground

► The primaries are assumed to be high
enough photons from outer space

► Search for diurnal and annual intensity
variations

► Study of energy homogeneity

Early particle physics (1930-1947):

► Direct observation of the primaries is
not yet possible, but the “latitude effect”
shows they are charged particles

► Trajectories of secondary charged parti-
cles are observed with cloud chambers
and counter telescope arrays, and momen-
tum is measured by curvature of trajectory
in a magnetic field

► Discoveries of positron and pair
production

► Soft and penetrating components

► Radiation processes and electromag-
netic cascades

► Meson theory of nuclear forces

► Discovery of mesotron (present day
muon)

► Properties of the muon, including mass,
lifetime and penetrability

► Two-meson theory and the meson
“paradox”

Later particle physics (1947-1953):

► Particle tracks observed in photograph-
ic emulsion

► Discovery of pion and v-p-e decay
chain

► Nuclear capture of negative pions

► Observation of primary cosmic-ray pro-
tons and fast nuclei

► Extensive air showers

► Discovery of the strange particles

► The strangeness quantum number

Astrophysics (1954 and later):

► Even now the highest energy particles
are in cosmic rays, but such particles are
rare

► Studies made with rockets and earth
satellites

► Primary energy spectrum, isotopic
composition

► X-ray and y- ray astronomy

► Galactic and extragalactic magnetic
fields

350

HISTORY OF PHYSICS

change of this much abused electron.

After Fermi’s successful theory of /?-
decay gave the neutrino a more legiti-
mate status than it had previously
enjoyed, there were attempts (although
not by Fermi) to incorporate electron-
neutrino pair exchange into the Hei-
senberg nuclear picture — the so-called
Fermi-field model. However, it was
shown to be impossible to fit simulta-
neously the range and strength of nu-
clear forces together with nuclear /?
decay. In an attempt to resolve this
conflict, Hideki Yukawa, in Japan,
made a bold imaginative stroke by
introducing a new theory of nuclear
forces that required the existence of a
new type of particle, a fundamental
massive boson.14 The particle was to
carry either the positive or negative
electronic unit charge, and its ex-
change was to be the agent of Heisen-
berg’s charge-exchange nuclear force.
From the range of nuclear forces its
mass was determined to be about 200
electron masses. Furthermore,
Yukawa’s meson (as it later became
known) was to be capable of decaying
into an electron and neutrino, in accord
with Yukawa’s proposed mechanism
for nuclear /? decay. Finally, it was
predicted to be a part of the cosmic-ray
flux.

In 1937 Anderson and others disco-
vered in cosmic rays both positive and
negative charged particles with masses
about 200 times that of the electron.
Some researchers greeted this as a
fulfillment of Yukawa’s prediction.15
A number of properties of these parti-
cles, including mass, charge and life-
time, were determined before or during
World War II; properties such as spin
and parity, and the characteristics of
interactions, were not determined un-
ambiguously until the large accelera-
tors came into use at the turn of the
1950s.18 The fact that the known pro-
perties, other than the charge, did not
provide a satisfactory match between
the meson observed in cosmic rays and
Yukawa’s postulated meson of nuclear
force stimulated new field theories that
went beyond QED.

Because these new field theories had
even worse divergence difficulties than
QED, and because their strong interac-
tions made perturbation methods far
more questionable, there again arose
practical as well as esthetic demands
for curing or circumventing “the infini-
ties” of field theory. The theoretical
struggle was double-pronged: One ef-
fort was to find a version of meson
theory that agreed with the cosmic-ray
meson’s behavior; another was to find a
meson theory to fit the nuclear forces,
whose complicated behavior came to be
better known. An important success of
the second approach was Nicholas
Kemmer’s symmetric meson theory of
nuclear forces, which established the

utility of the concept of isospin and
called for the existence of a charged
triplet of positive, negative and netural
mesons.16 The neutral meson, whose
two-photon decay initiates the majority
of cascade showers in the cosmic rays,
was not observed until it was artificial-
ly produced in 1950.

Admitting a new particle. The cosmic-
ray meson (muon) is the main compo-
nent of the hard or penetrating cosmic
rays. The penetrating rays were seen
as early as 1929 in the first absorption
measurements made on individual cos-
mic-ray particles, and perhaps were
suggested by even earlier measure-
ments. But it was not until 1937 that
Seth Henry Neddermeyer and Ander-
son claimed these cosmic-ray mesons to
be new charged particles — neither elec-
trons nor protons — on the basis of their
ability to penetrate a 1-cm thickness of
platinum.4 Even though scientists else-
where, in England and France for ex-
ample, were making similar observa-
tions, the preferred interpretation was
that QED breaks down at high ener-
gies. That was the view of Blackett,
who called the particles electrons and
considered that a modification of the
radiation formulas was in order.17 Two
French cloud-chamber groups empha-
sized that there were “two species of
corpuscular rays” (like Anderson’s red
and green electrons) differing in their
penetrating power; however, they did
not insist on any new particles.18 Two
observations of mesons stopping in the
gas of a cloud chamber permitted a
determination of their masses suffi-
cient to show them to be roughly 200
times the electron mass, or about one-
tenth of the proton mass.19

The next step was to deal with the
problem posed by the false identifica-
tion of the muon with Yukawa’s nu-
clear meson: If the cosmic-ray meson
were Yukawa’s strongly interacting
particle, why did it not seem to interact
at all? The remaining story of the
muon — the determination of its mass,
lifetime and interaction properties, and
the growing sense of bewilderment and
paradox in the confrontation between
experiment and theory — was climaxed
when an Italian group proved that
negative muons stopping in carbon de-
cay before they can be captured by the
nucleus.20

The grand finale came when a group
at Bristol University in England used a
new nuclear photographic emulsion
technique to reveal the pion, Yukawa’s
nuclear meson, and its decay into the
muon, the cosmic-ray meson.21 How-
ever, the solution of the v-fi paradox
produced a new one, the “muon puz-
zle”: making sense of the evidence that
the muon was a heavy version of the
electron — in modern terms, a second-
generation lepton. The observation of
the complete decay chain, pion— >muon

—►electron, together with the long
muon lifetime, strongly suggested this
similarity. Today this is known as the
puzzle of the “generations” of quarks
and leptons.

Unification and diversification

Many physicists today believe that
we are approaching a new synthesis in
our view of matter, in which the world
will be seen as made up of a few types of
elementary particles that interact by
means of a small number of forces, with
both particles and forces being aspects
of a few or perhaps even a single
quantum field. An important reason
for this confidence in unification is the
apparent success of the theory of the
unified electroweak field. The 1979
Nobel lectures in physics deal with this
subject and with speculative theories of
a more advanced type, having names
such as “electronuclear grand unifica-
tion” and “extended supergravity.”

The mood of those lectures is one of
barely qualified optimism.22 Sheldon
Glashow, for example, while cautioning
against the adoption of a “premature
orthodoxy,” contrasts the present with
1965, when he began theoretical phy-
sics and when “the study of elementary
particles was like a patchwork quilt.”
He continues:

Things have changed. Today we
have what has been called a “stan-
dard theory” of elementary parti-
cle physics in which strong, weak,
and electromagnetic interactions
all arise from a local symmetry
principle. It is, in a sense, a com-
plete and apparently correct the-
ory, offering a qualitative descrip-
tion of all particle phenomena and
precise quantitative predictions in
many instances. There are no ex-
perimental data that contradict
the theory. In principle, if not yet
in practice, all experimental data
can be expressed in terms of a
small number of “fundamental”
masses and coupling constants.
The theory we now have is an
integral work of art: The patch-
work quilt has become a tapestry.
These remarks are reminiscent of
other far-reaching syntheses: not only
the “mechanical philosophy” of the
eighteenth century and the “electro-
magnetic synthesis” at the end of the
nineteenth century, but also physics as
it appeared about 50 years ago. Then it
was believed that there were only two
fundamental material particles (elec-
tron and proton), only two fundamental
forces (gravitation and electromagne-
tism), and that the fundamental laws
were known (relativity and quantum
mechanics). Accordingly, as Stephen
Hawking reports, shortly after Dirac
published his relativistic wave equa-
tion for the electron, Max Born said
that “Physics, as we know it, will be

PARTICLES AND QUANTA

351

Lunches at the Niels Bohr
Institute in Copenhagen.
These photos, taken in
1 934, show (at right)
Walter Heitler with Leon
Rosenfeld and (below)
Werner Heisenberg and
Niels Bohr. (Photos
courtesy Paul Ehrenfest Jr )

over in six months.23

Although the positron discovery of
August 1932 was a validation of Dirac’s
theory, that particle (and the neutron,
neutrino and meson) totally destroyed
the synthesis that appeared to be at
hand in 1930. As Millikan said: “Prior
to the night of 2 August 1932, the
fundamental building-stones of the
physical world had been universally
supposed to be simply protons and neg-
ative-electrons.”24 Progress in the
1930s and the next few decades would
lie not in unification of forces and
reduction in the number of elements
but rather in diversification — the dis-
covery of new particles, the enlarge-
ment of the particle concept and the
recognition of new nuclear forces, both
strong and weak. During the 1930s and
1940s there were discovered the first
antiparticle (the positron), the second
baryon (the neutron), the second lepton
(the muon), a neutral massless lepton
(the neutrino, although actually first
detected in 1953), the first massive field
quanta, both charged and neutral (the
pions), and the strange particles. By
1950, the modern idea of families of
particles and the distinction between
hadrons and leptons had already
emerged. The idea of the universal

weak interaction was also in the air.
For hadrons there was the beginning of
what Victor Weisskopf has called the
“third spectroscopy” (that is, after
those of atoms and nuclei), although all
three cases involve not only spectrosco-
py but also structures. Thus the path
toward unification, which looked at-
tainable for a few years after resolution
of the n-fi paradox, now seemed to twist
through a minefield of the most diverse
phenomena.

Particles and human attitudes

Because of their fundamental and
universal character, elementary parti-
cles (and their unexpected properties
such as indeterminacy, complementar-
ity, strangeness and spin) both influ-
ence and are influenced by our general
world outlook, from our primitive per-
ceptions to our most advanced philoso-
phical conceptions. Space limitations
allow us only a glance at these issues,
which we explore more fully in the
symposium volume on which this arti-
cle is based.

Some of the greatest battles occurred
in the 1930s and 1940s over the en-
largement of the concept of elementary
particles far beyond the Newtonian
mass point. Two of these battles in-

volve the neutron and the neutrino and
belong also to nuclear physics. At the
Minnesota symposium, Maurice Gold-
haber recalled:

I remember being quite shocked
when it dawned on me [in 1934]
that the neutron, an “elementary
particle” as I had by that time
already learned to speak of it,
might decay by /remission with a
half-life that I could roughly esti-
mate ... to be about half an hour
or shorter ... 1

The battles over the positron and
over the two mesons illustrate the psy-
chological resistance of physicists to
admit new particles to their cherished
scheme. Dirac, in his first paper on the
positron, and Anderson, in tune with
what he called the “spirit of conserva-
tism,” both initially identified this new
particle as a proton. Dirac even tried to
make an argument for increasing the
positron mass to the size of the proton
mass; he realized that the new particles
could not be protons only after Her-
mann Weyl proved mathematically
that the holes had to have the same
mass as electrons.

Yukawa had virtually no support
outside Japan for his proposed nuclear
meson until the mu meson was ob-
served. Bohr’s response to the proposal
by the Kyoto group that there is a
neutral meson in addition to the
charged one was “Why do you want to
create such a particle?” And the tanta-
lizing rr-fi paradox during 1937-1947
arose out of the reluctance to admit
that there could be a second particle,
having a mass similar to that of the
Yukawa particle but in other respects
behaving differently.

Researchers in the 1930s and 1940s
were strongly affected by the over-
whelming economic, social and politi-
cal upheavals of that period. To list but
a few:

► the economic depression, which took
away jobs and financial security

► the rise of fascism in Europe, which
displaced many physicists (including

352

HISTORY OF PHYSICS

Development of quantum
field theory

Prehistory

Classical (19th century):

► Electromagnetism (Faraday, Maxwell,
Hertz, Lorentz)

Quantum (1900-1927):

► Blackbody radiation (Planck, 1900)

► Photon hypothesis (Einstein, 1905)

► Stationary states of atom (Bohr, 1913)

► Atomic emission and absorption coeffi-
cients (Einstein, 1916)

► Bose and Fermi statistics (1924)

► Electron waves (de Broglie, 1924)

► Exclusion principle and spin (Pauli,
Goudsmit, and Uhlenbeck, 1925)

► Quantum mechanics of atoms and mol-
ecules (Heisenberg, Schrddinger, Dirac,
Born, 1925-1926)

► General transformation theory (Dirac,
1927)

Birth and early development (1927-
1929):

► Quantum electrodynamics (QED)
(Dirac, 1927)

► Second quantization (Jordan and Klein,
1927, and Jordan and Wigner, 1928)

► Relativistic electron theory (Dirac, 1 928)

► Relativistic QED (Heisenberg and Pauli,
1929)

► Theory of holes (Dirac, 1929)

Developments, difficulties and doubts

(1929-1934):

► Applications of QED and Dirac theory
(Klein and Nishina, 1929; Oppenheimer et
at:, Bethe and Heitler, 1934)

► Experimental tests (Meitner and Hup-
feld, 1930, Tarrant, Gray, Chao)

► Specter of infinite energy shifts (Oppen-
heimer, 1930)

► Specter of infinite vacuum polarization
(Dirac, 1932)

New fields (1934-1946):

► Scalar field theory (Pauli and Weiss-
kopf, 1934)

► Beta decay theory (Fermi, 1934)

► Meson theory of nuclear forces
(Yukawa, 1935)

► Relativistic spin-one theory (Proca,
1936)

► “Infrared” radiation (Bloch and Nord-
sieck, 1937)

► S-matrix (Wheeler, 1937, and Heisen-
berg, 1943)

► Developments of meson theory (Frdh-
lich, Heitler, Kemmer, Yukawa, Sakata,
Taketani, Kobayasi, 1938)

Renormalization (1947 and later):

► Lamb shift (Lamb and Retherford, 1 947)

► Calculation of Lamb shift (Bethe, 1 947)

► Electron magnetic moment (Foley and
Kusch, 1948)

► Renormalized relativistic QED (Tomon-
aga, Schwinger, Feynman, Dyson, 1948-
1949)

Weisskopf, Bethe, Fermi, Rossi and Ru-
dolf Peierls) from their homes in Ger-
many and Italy, and at the same time
dissolved much of the research estab-
lishments in those countries

► the political controls on philosophy
(including physics) in certain countries

► the brutal war, with its diversion
from research to defense work

► its bombings and destruction

► the death camps

► the economic shortages

► the breakdown of communications
between countries

► the occupations.

Other authors have dealt with these
developments, but their effects on phy-
sics have not yet been fully examined.
Many vital social issues have not been
considered. For example, the postwar
occupations had a definite impact on
physics. In Japan, the American occu-

pation in 1945-1951 slowed nuclear-
physics research by explicitly prohibit-
ing experimental nuclear physics. Yet
at the same time the occupation helped
to establish the institutional basis for
Japan’s rapid progress in nuclear phy-
sics during the 1950s and 1960s.

In the postwar period, particle phy-
sics grew very rapidly, as did other
subfields of physics. Many factors con-
tributed to this postwar boom:

► the greater internationalism of
science resulting from the war

► new experimental techniques devel-
oped as part of the weapons programs

► new funding mechanisms that
emerged from the wartime support for
research, resulting in, for example, the
National Science Foundation and the
Atomic Energy Commission

► the new widespread appreciation
of the value of science for national
security

► the sudden reentry into physics of
graduate students and other research-
ers who, after about four years away,
were anxious to make up for lost time

► the closer relationship between the-
ory and experiment resulting from the
experience of the large wartime pro-
jects such as building the bomb and
developing radar for defense.

These and other influences need to be
illuminated in detailed scholarly stu-
dies, for such larger issues are insepa-
rable from the intellectual develop-
ment of physics. Scholars will need to
probe them deeply to understand fully
the birth of particle physics.

This article is an abridged version of the in-
troductory essay to the proceedings of the In-
ternational Symposium on the History of Par-
ticle Physics, held at Fermilab 28-31 May
1980. The Proceedings were published in
1983 as The Birth of Particle Physics ( Cam-
bridge U.P., New York).

Robert Millikan (center) visits Seth Neddermeyer (right) and Carl cloud-chamber experiment. The photograph was taken in 1935
Anderson on the summit of Pike’s Peak, where Anderson set up his (Courtesy of Carl Anderson.)

PARTICLES AND QUANTA

353

Hideki Yukawa and Richard Feynman during Feynman’s visit to Kyoto, Japan, in the summer of
1955. Left to right: Mrs. Yukawa, Satio Hayakawa, Feynman, Yukawa, Koichi Mano, Minoru Ko-
bayasi. (Courtesy of Satio Hayakawa.)

References

1. H. Steuwer, ed., Nuclear Physics in Retro-
spect; Proceedings of a Symposium on the
1930s, U. of Minnesota P., Minneapolis
(1979).

2. W. Kolhorster, Naturwiss. 16, 1044
(1928); W. Bothe and W. Kolhorster,
Naturwiss. 16, 1045 (1928).

3. D. Skobeltzyn, Z. f. Phys. 43, 354 (1927);
54, 686 (1929).

4. C. D. Anderson, Science, 76, 238 (1932); S.
H. Neddermeyer, C. D. Anderson, Phys.
Rev. 51, 884 (1937).

5. P. M. S. Blackett, G. P. S. Occhialini, Proc.
Roy. Soc. A139, 699 (1933)

6. P. A. M. Dirac, Proc. Roy. Soc. (London)
A114, 243 (1927).

7. P. Jordan, E. Wigner, Z. f. Phys. 47, 631
(1928).

8. Gregor Wentzel, in Theoretical Physics in
the Twentiety Century, M. Fierz, V. F.
Weisskopf, eds., Interscience, New York
(1960).

9. W. Heisenberg, W. Pauli, Z. f. Phys. 56, 1
(1929); 59, 168 (1930), Part II.

10. O. Klein, Y. Nishina, Z. f. Phys. 52, 853
(1929).

11. H. Bethe, W. Heitler, Proc. Roy. Soc.
(London) A146, 83 (1934). (Italics of Bethe
and Heitler.)

12. E. J. Williams, Proc. Roy. Soc. (London)
A139, 163 (1933); Phys. Rev. 45, 729
(1934); K. Danske Vid. Selskab (Math.-
Phys. Meddelelser) 13, No. 4, 1 (1935); C. F.
von Weizsacker, Z. f. Phys. 88, 612 (1934).

13. H. J. Bhabha, W. Heitler, Proc. Roy. Soc.
(London) A159, 432 (1937); J. F. Carlson,
J. R. Oppenheimer, Phys. Rev. 51, 220
(1937).

14. H. Yukawa, Proc. Phys.-Math. Soc. Ja-
pan 17, 48 (1935).

15. J. R. Oppenheimer, R. Serber, Phys. Rev.
51, 1113 (1937); E. C. G. Stueckelberg,
Phys. Rev. 52, 41 (1937).

16. N. Kemmer, Proc. Camb. Phil. Soc. 34,
354 (1938).

17. P. M. S. Blackett, J. G. Wilson, Proc. Roy.
Soc. (London) A160, 304 (1937).

18. J. Crussard, L. Leprince-Ringuet, Compt.
rend. 204, 240 (1937); P. Auger, P. Ehren-
fest Jr, Journ. de Phys. 6, 255 (1935).

19. J. C. Street, E. C. Stevenson, Phys. Rev.
51, 1005 (1937); Y. Nishina, M. Takeuchi,
T. Ichimiya, Phys. Rev. 52, 1198 (1937).

20. M. Conversi, E. Pancini, O. Piccioni,
Phys. Rev. 71, 209 (1947).

21. C. M. G. Lattes, H. Muirhead, G. P. S.
Occhialini, C. F. Powell, Nature 159, 694
(1947).

22. S. Weinberg, Rev. Mod. Phys. 52, 515
(1980); A. Salam, Rev. Mod. Phys. 52, 525
(1980); S. L. Glashow, Rev. Mod. Phys. 52,
539 (1980).

23. S. Hawking, Is the End in Sight for
Theoretical Physics, Cambridge U. P.,
New York (1980).

24. R. A. Millikan, Electrons, Cambridge U.

P., New York (1935), page 320. □

HISTORY OF PHYSICS

the Discovery of

ELECTRON TUNNELING

into SUPERCONDUCTORS

By Roland W. Schmitt PHYSICS TODAY / DECEMBER 1961

IN August 1960, Ivar Giaever published a discovery
about electron tunneling into superconductors 1 :
the discovery was elegant and had the esthetic
simplicity that makes a scientist wonder why it had
not been made before. It is too early to assess the
importance of the discovery; it may be recorded as
only a small but neat strand of science, or the train
of work it has set off may produce a web of new
knowledge about solids. Regardless of the final assess-
ment that science makes of it, the discovery was sur-
rounded by novel circumstances that dramatize the
unexpected course of discovery.

Other physicists had come close to making the
discovery or seemed on the verge of doing so: some
had been doing similar experiments, but missed the
discovery; some were looking for the wrong effect
because of mistaken ideas; some were experimenting
in the same field and, though not looking for a par-
ticular effect, could have stumbled on it. The experi-
ment could have been done with equipment and tech-
niques that were common a decade ago; it was not
blocked by inadequate techniques and did not have
to wait for the development of new research tools. Only
a simple vacuum system for evaporating thin metallic
films, a voltmeter, ammeter, and liquid helium were
needed. The discovery was technically an easy one.
Why, then, did the experiment remain undone during
the previous decade while many physicists were work-
ing on superconductivity, including thin films? In spite
of being simple, of being unblocked by technical com-
plexities, of being in the arena of attention of many
physicists, the discovery remained unsought and un-
detected until it was looked for and found by a young
mechanical engineer just changing to a career in physics.

This story is the story of the discovery and the dis-
coverer. I have only two reasons — other than the appeal
of an entertaining story about research — for writing
about the details of this microcosm in the history of
science. Occupying an administrative post close to the
people who played roles in the discovery, I had an
intimate, but detached, view of the events that oc-
curred. Also, in this story it is reasonably clear what
was discovered and when it was discovered; what was
new did not emerge slowly through the hazy fringes

Roland W. Schmitt is a physicist in the Metallurgy and Ceramics
Research Department of the General Electric Research Laboratory,
Schenectady, N. Y.

of discovery nor was it ciouaed by almost indistin-
guishable parallel discoveries. Goudsmit’s fear that
“when we try to look at a recent event with a micro-
scope, the resolving power may often be insufficient” 2
does not hover too ominously in the background of this
story. Except for these particular reasons, I make no
claim that this story ought to be told any more than
the stories of hundreds of other discoveries that go
unreported.

THE history of superconductivity is a checkered
one; it is characterized by long lapses between the
major experimental discoveries and by an extraordinary
hiatus between the original discovery and the first ac-
ceptable, fundamental theory of the phenomenon.
Kammerlingh Onnes, in 1911 at Leiden, discovered
superconductivity and found the characteristic property
of zero resistance; he also learned that a high magnetic
field would destroy superconductivity so that the state
existed only at very low temperatures and in low
magnetic fields. Another bulk property of superconduc-
tors remained hidden until 1933, when Meissner in
Germany found it: in low magnetic fields, supercon-
ductors are perfect diamagnetics and expel all magnetic
flux from their interior. The fundamental theory of the
phenomenon still could not be developed in spite of
intense efforts, but in 19 SO the discovery of the isotope
effect — a variation in the superconducting transition
temperature with isotopic mass — confirmed an emerging
suspicion of several theoreticians: that the interaction
of electrons with lattice vibrations played the key role
in producing superconductivity. Nevertheless, not until
1957, forty-six years after the original discovery, did
Professor John Bardeen and two of his associates, Leon
Cooper and J. Robert Schrieffer, develop a satisfactory
theory of superconductivity.

One feature of this theoretical development is espe-
cially interesting for the story of electron tunneling
into superconductors. The BCS theory, as it has come
to be known, showed that a small but nonzero energy
difference separated the first excited state of a super-
conductor from the ground state. Translated into the
usual one-electron picture that physicists use when
thinking about metals, this feature becomes a forbidden
energy gap centered at the Fermi energy; in a super-
conductor, no electrons can have energies in this
forbidden range.

PARTICLES AND QUANTA

355

(a) The tunneling current between two normal
metal films varies linearly with voltage at low
voltages. As the voltage is increased, more and
more filled levels of the metal film with negative
bias are exposed (through the thin insulating bar-
rier) to empty levels in the opposed metal film.
This permits more and more electrons to tunnel
through the barrier into empty states.

lb)

(b) The discovery. The forbidden energy gap at
the Fermi level in superconductors prevents elec-
trons from tunneling through the barrier into the
superconductor until the biasing voltage exceeds
half the gap width. The shape of the current-volt-
age curves measures the gap width and the density
of states near the gap. The curve in this figure
corresponds to T = 0.

Speculations about this energy gap reach back
twenty years into the history of superconductivity,
and experiments to detect it engaged physicists both
before and after the BCS theory. The most convincing
evidence for the gap came from studies of the way
infrared radiation passed through or was absorbed by
very thin films of superconductors.3 These studies,
carried out by Professor M. Tinkham and his students
at Berkeley, demanded the most skillful experimental
techniques; they needed talented experimentalists for
their success.

The presence of the forbidden gap in superconductors
means that if one tries to inject electrons with the
forbidden energies into a superconductor, they will be
rejected by it. Giaever showed this to be true with his
experiment; it gave the most simple, direct evidence for
the existence of the energy gap in superconductors and
also gave information about the behavior of electrons
with energies near the gap. The experiment is to inject
electrons into a superconductor by letting them tunnel
through a very thin, insulating barrier. Such a barrier
allows one to vary the potential difference between the
metal from which electrons are drawn and the metal
into which they are injected and, therefore, makes it
possible to vary the injection energy. Furthermore, the
barrier prevents the free flow of electrons from the
metal into the superconductor, as would occur with
direct contact, but still allows single electrons to move
through it one at a time. The original experiment used
a thin, evaporated, aluminum film, coated with its own
oxide and topped by another thin, evaporated film of
lead. At the boiling point of helium, the lead, but not
the aluminum, is superconducting. At very low volt-
ages, almost no current flows through the junction be-
cause the energy of the injected electrons is in the
forbidden energy range of electrons in the supercon-
ductor, but the current grows rapidly as the voltage

Experimental results showing tunneling current be-
tween aluminum and lead at various temperatures.
At 10°K neither metal is superconductive, between
4.2°K and 1.3°K only lead is superconductive, and
below 1.3 °K both are superconductive.

356

HISTORY OF PHYSICS

reaches a value equal to half the width of the for-
bidden gap, for then the injection energies are equal
to the allowed energy values in the superconductor.
The current-voltage curve reveals directly the existence
of the energy gap in superconductors and permits a
simple measure of the size of this gap. With this ele-
mentary experiment, Giaever not only opened a new
realm of experimental work on superconductors, but
also created the hope of further discoveries about
tunneling into metals, semimetals, and semiconductors.

The story behind the discovery begins in 1957. John
C. Fisher became interested in the electronic properties
of thin films; he talked about experimental possibilities
with several people in our research group, but, because
his main interest was different, there was no further
activity until the latter part of 1958 when Giaever
joined the section.

GIAEVER was born and educated in Norway; in
1954 he emigrated to Canada as a mechanical
engineer. There he worked for a while as an architect’s
aide, but soon joined the Canadian General Electric
Company. In 1956, he came to Schenectady in order
to follow an advanced training program for engineers.
During this period he had one assignment of six months
at the General Electric Research Laboratory and
worked on a problem of heat flow — a problem in ap-
plied mathematics associated with an applied-research
project. During this time Giaever noticed that there
w'ere solid-state physicists at the Laboratory who were
working on problems that seemed to be more interesting
to him than the problems of engineering. Near the end
of his assignment he asked if he could switch fields
and try to become a physicist.

He joined our group, a group devoted to solid-state
physics research, in September 1958 and began work
under John Fisher. At the same time, Giaever began
taking advanced courses in physics at Rensselaer Poly-
technic Institute in Troy, N. Y. These studies were
to prove critical in the discovery.

Fisher and Giaever began their work on thin films
with Langmuir Aims; they tried, by various techniques,
to put metallic electrodes on opposite sides of mono-
molecular layers and to measure electrical conductance
through them. This technique proved so cumbersome
and unreliable that after a few months they abandoned
it and turned to evaporated-film junctions of aluminum-
aluminum oxide-aluminum. With these Aims they did
a series of experiments measuring the relation of
electrical current through the oxide Aim with Aim thick-
ness, voltage, and temperature, and showed that electron
tunneling caused the current through the barriers 4.
During the year occupied with this work, Giaever
learned both physics and experimental techniques, and
by the end of 1959 he was carrying most of the work
forward while Fisher’s main efforts remained with
other problems; nevertheless, Fisher continued to be
the main source of stimulation, ideas, and criticism
other than Giaever himself.

Aluminum is a superconductor if cooled below 1.2°
K, and it may have been because of this fact alone,
and for no better reason, that it was Arst suggested that
the A1-AL03-A1 junctions be cooled to see what effect,
if any, superconductivity would have on the tunneling
current. The origin of the question, “Why don’t you
cool them to superconducting temperatures?” is lost;
the question is of a type continually being asked in an
active research group, and several people asked it at
one time or another. Each time Giaever rejected the
suggestion, because, he argued, most of the junction
resistance was in the barrier itself and a vanishing
resistance of the metal Alms would make no important
difference to the junction current. In the light of sub-
sequent events this argument may seem astonishing,
yet no one in the preceding decades had joined a
conception of the experiment with a reason for doing
it, and it is not surprising that Giaever did not at
Arst do so. In any case, he could not at that time have
seen the real reason for doing the experiment, for he
did not know of the energy gap at the Fermi level in
superconductors! He had not, in one year as a physi-
cist, learned all of the things that a person with
conventional training would be expected to know, and
none of the solid-state physicists among whom he
worked had mentioned the superconducting energy gap
in a way that had caught his attention.

Early in the spring of 1960, the question about cool-
ing the junctions to superconducting temperatures was
asked again, and this time it almost coincided with the
study of superconductivity in a course at RPI. There
Giaever learned of the energy gap; he recognized that
this gap could have an effect on the tunneling current
and suggested this possibility to John Fisher, Charles
Bean, and Walter Harrison. The Arst reaction of all
three was that probably the gap would not be notice-
able. It was, after all, quite small and was only a crude
representation of a more complex, many-electron effect;
one could not take the simple picture, so like the

Ivar Giaever, Walter Harrison, Charles Bean, John Fisher.

PARTICLES AND QUANTA

357

THERMALLY
EXCITED \
ELECTRONS

\

DENSITY OF
^ STATES

k

1 ENERGY GAP

" HOLES’^'

—

EEEEE

L — ^

—

(B)

ICI

Tunneling between two different superconduc-
tors. (A) The two superconductors with no
voltage applied. Thermally excited electrons
above and holes below the gaps are shown.
(B) When a voltage is applied, the thermally
excited electrons in the left superconductor can
tunnel into empty levels above the gap of the
right superconductor. (C) When the voltage is
increased further, only the same number of
electrons may flow and they now face a lower,
less favorable density of states in the right
superconductor. The current decreases as a
function of voltage until the electrons below
the gap of the left superconductor are lifted
enough to flow into the levels above the gap
of the right superconductor.

picture of a semiconductor, too literally. Nevertheless,
they all urged Giaever to try the experiment, and he
soon calculated the width of a gap in units one would
use in the experiment — in volts. Until then, none of
us had noticed (at a time when it would have been
meaningful) that superconducting gap widths are in
the millivolt range, yet this simple fact was critical at
that delicate moment when the experimenter had to
decide whether to go ahead or not.

Giaever chose an aluminum-aluminum oxide-lead
junction but failed to get definitive results in the first
few trials. But, by this time, the conviction that there
should be an effect was strong enough to carry the
work on, and these efforts were shortly rewarded with
success. Within a day or two of this success, Giaever
and Charles Bean, who recognized the possible import
of the experiment and began to work with Giaever,
noticed that a simple model of the electron tunneling
allowed them to deduce the density of states near the
gap in a superconductor from the shape of the current-
voltage curves. This observation suggested that elec-
tron-tunneling experiments might yield the density of
states near the Fermi energy in normal metals and semi-
metals. Also, Giaever quickly recognized that tunneling
between two superconductors should yield dynamic
negative-resistance regions in the voltage-current char-
acteristics. The second of these predictions has proved
to be correct, and, following Giaever’s publication of
the original discovery1, scientists at Arthur D. Little
Company also recognized the possibility, and they, as
well as Giaever, proved it to be true 5' 6. The hope that
tunneling experiments could measure the density of
states in normal metals and semimetals became dim
after detailed theoretical studies of Walter Harrison
gave results different from the first, intuitive model.
Subsequent experiments have failed to show interesting
behavior, but all hope for some effects has not been
abandoned.

By now, this discovery has firmly entered the science
of superconductivity. It has also broadened the pos-
sibilities of other work on tunneling — technological as
well as scientific — beyond the realm of semiconductors.

JN the end it is not possible to answer the question
asked at the beginning of this story: why did this
elegant experiment, one that is so easy to do, remain
undone during the previous decade? Sir C. G. Darwin
has said of the discovery of atomic numbers that it
was an “easy” discovery, meaning that “when dis-
covered, it is so easy to understand that it is difficult
afterwards to see how people had got on without it” 7.
This kind of discovery, with its birth, destroys un-
recognized barriers to the discovery that cannot subse-
quently be recreated or imagined. In this sense,
Giaever’s discovery was also an easy one.

Some of the ingredients that led to success are
apparent in the story of the discovery: there was a
question asked, catalyzing the reaction of knowledge
about superconductors with experiments on electron
tunneling; there was a delicate balance between
theoretical knowledge and naivete; there was a pre-
disposition for working with simple, uncomplicated
equipment; there was the permissive attitude of more
senior research people. Chance played a role in ar-
ranging these factors, but to no greater extent than it
plays a daily role in the research of every scientist;
in spite of these ingredients the discovery could have
been missed. The final key was that Giaever deliberately
tried to make the discovery, and, in the end, knew
why he wished to do the experiment and what he was
looking for. This fact is probably the crucial fact that
caused him to succeed while other scientists in a
position to make the discovery did not.

Other discoveries have been made in other ways and
the story of this one is not a prescription. But it is a
reminder that even in this age of complexity there
remain simple, but important, discoveries to be made.

References

1. Giaever, I., Phys. Rev. Letters 5, 147 (1960).

2. Goudsmit, S. A., Physics Today, June 1961, p. 18.

3. Glover, R. E., Ill and Tinkham, M., Phys. Rev. 108, 243 (1957).

4. Fisher, J. C. and Giaever, I., J. Appl. Phys. 32, 172 (1961).

5. Nicol, J., Shapiro, S. and Smith, P. H., Phys. Rev. Letters 5,
461 (1960).

6. Giaever, I., Phys. Rev. Letters 5, 464 (1960).

7. Darwin, Charles, Proc. Roy. Soc. A236, 285 (1956).

358

HISTORY OF PHYSICS

Victor F. Weisskopf

Victor Weisskopf is Institute
Emeritus Professor of physics
at MIT. From 1961-1965 he
was Director General of CERN.

This article is devoted to the de-
velopment of quantum field theory,
a discipline that began with quan-
tum electrodynamics,1 which was
born in 1927 when P. A. M. Dirac
published his famous paper “The
Quantum Theory of the Emission
and Absorption of Radiation.” Fig-
ure 1 reproduces the first page.
Note that it was communicated by
Niels Bohr himself. Also note the
second and third sentences. The
latter is an understatement indeed:
Nothing had been done up to this
time on quantum electrodynamics.

The pre-Dirac time

Classical electrodynamics start-
ed in 1862 when James Clerk
Maxwell created his equations
connecting the electric field E and
the magnetic field B with the
charge density p and the current
density j. Together with the ex-
pression of the Lorentz force act-
ing on a system carrying charge
and current in an electromagnetic
field, it led to an understanding of
light as an electromagnetic wave,
of the radiation emitted by moving
charges and of the effects of radi-
ation upon charged bodies. The
results were splendidly verified by
Heinrich Hertz in 1885 for radi-
ations emitted and absorbed by
antennas.

The application to atomic radi-
ation was stymied by two facts:
First, p and j in atoms were un-
known to them; second, they
faced a fundamental difficulty
when the statistical theory of heat
was applied to the radiation field.
The number of degrees of free-

PHYSICS TODAY / NOVEMBER 1981

The development
of field theory in
the last 50 years

dom of a radiation field in a unit
volume is infinite, and if each de-
gree is supposed to get an energy
kT/2 according to the equipartition
theorem, the total energy density
becomes infinity; empty space
would be an infinite sink of radi-
ation energy. Furthermore, apart
from this distressing result, the
classical theory of light had no ex-
planation of the daily experience
that incandescent matter changes
its color with rising temperature—
from red to yellow and then to
white. The physicists must have
felt before 1 900 much as the neur-
ophysiologists of today feel with-
out any explanation of what mem-
ory is.

Then came quantum theory. It
developed with increasing speed
within a quarter century beginning
with Max Planck’s insight into the
nature of blackbody radiation in
1900, followed by Albert Einstein’s
revolutionary idea of the existence
of a photon in 1905, by Niels
Bohr’s atomic model in 1913, and
by Louis DeBroglie’s daring hy-
pothesis of the wave-particle dual-
ity of particles in 1924. It reached
its peak with the formulation of
quantum mechanics by Werner
Heisenberg, Erwin Schrodinger,
Dirac, Wolfgang Pauli and Bohr in
1925.

The difficulties of the classical
theory disappeared with one
stroke — not without bringing about
other difficulties about which much
more will be said soon. Of
course, the problem of heat radi-
ation was immediately solved and
the reasons for the sharp charac-
teristic spectral lines of each
atomic species became evident.

Atomic stabilities, sizes and excita-
tion energies could be derived
from first principles: The chemical
forces turned out to be a direct
consequence of quantum mechan-
ics; chemistry became part of
physics.

However, before the publication
of Dirac’s 1927 paper, it was not
possible to derive the expressions
for p and j within the atoms for the
purpose of calculating the emis-
sion of light quanta.

Actually, the Schrodinger equa-
tion allowed the calculation of
transitions under the influence of
an external radiation field, that is
the absorption of light and the
forced emission of an additonal
photon in the presence of an inci-
dent radiation. The field of an in-
cident light wave could be consid-
ered as a perturbation on the atom
in the initial state; it was possible
by means of the Schrodinger
equation to calculate the probabil-
ity of a transition, which turned out
to be proportional to the intensity
of the incident light wave. Howev-
er, the emission by a transition
from a higher to a lower state in a
field-free vacuum could not be
treated. It was assumed at that
time the matrix elements (a\p\by
and <a|j|6> between two station-
ary states a , b of the atom play
the role of charge and current
density responsible for the radi-
ation connected with the quantum
transition from a to b or vice
versa. The atom was considered
as an “orchestra of oscillators,”
and the matrix elements deter-
mined the strengths of those oscil-
lators ascribed to each pair of
states. To determine the intensity

359

AIR NIELS BOHR LIBRARY

The Quantum Theory of the Emission and Absorption of
Radiation.

By P. A. M. Dirac, St. John’s College, Cambridge, and Institute for
Theoretical Physics, Copenhagen.

(Communicated by N. Bohr, For. Mem. R.S.— Received February 2, 1927.)

§ 1 . Introduction, and Summary.

The new quantum theory, based on the assumption that the dynamical
variables do not obey the commutative law of multiplication, has by now been
developed sufficiently to form a fairly complete theory of dynamics. One can
treat mathematically the problem of any dynamical system composed of a
number of particles with instantaneous forces acting between them, provided it
is describable by a Hamiltonian function, and one can interpret the mathematics
physically by a quite definite general method. On the other hand, hardly
anything has been done up to the present on quantum electrodynamics. The
questions of the correct treatment of a system in which the forces are propa-
gated with the velocity of light instead of instantaneously, of the production of
an electromagnetic field by a moving electron, and of the reaction of this field .
on the electron have not yet been touched. In addition, there is a serious
difficulty in making the theory satisfy all the requirements of the restricted

Title page of paper (below) by
P. A. M. Dirac (left) on radiation
theory (from Proceedings of the
Royal Society 114, 243,

1927). Figure 1

of spontaneous emission, one had
to use either the oscillator model
and equate the emission with the
classical radiation of these oscilla-
tors, or one had to use the Ein-
stein relations, from which it fol-
lows that the probability of
spontaneous emission from b to a
is equal to the absorption probabil-
ity from a to b when the light inten-
sity per frequency interval da is
put equal to a certain value l0:

l0da =

tier

Av*C2

da

0)

This happens to be the light inten-
sity when each degree of freedom
of the radiation field contained one
photon. According to this rule the
probability of spontaneous emis-
sion is equal to the probability of a
forced emission by a fictitious radi-
ation field of the intensity 1 .

But why? According to the
Schrodinger equation, any station-
ary state should have an infinite
lifetime when there is no radiation
present.

Quantization of the
radiation field

Dirac’s fundamental paper in
1927 changed all that. Quantum
mechanics must be applied not
only to the atom via the Schro-
dinger equation, but also to the ra-
diation field. Dirac made use of
the old idea of Paul Ehrenfest
(1906) and Peter Debye (1910), to
describe the electromagnetic field
in empty space as a system of
quantized oscillators. In the pres-
ence of atoms or of other systems
of charged particles, the coupling
between the charged particles and
the field is expressed by an inter-
action energy

H' =ef\-Mx3 (2)

where j is the current density of
the particles. The value e of the
particle charge is inserted here as
an explicit factor and A is the vec-
tor potential. Both magnitudes
are operators in the quantized sys-
tem of the atom and the field os-
cillators. Expression 2 is a direct

360

HISTORY OF PHYSICS

consequence of Maxwell’s equa-
tions. The Hamiltonian of the
combined system then has the
form

H = H0 + H' (3)

H0 Afield Y ^atom

where A/fleld is the Hamiltonian of
the isolated field oscillators and
HaXom is the Schrodinger Hamilton-
ian of the atom isolated from the
electromagnetic fields.

The Hamiltonian H0 describes
field and atom without interac-
tion. The effects of /Y1 are treated
as a perturbation upon the system
H0. The stationary states of H0
are characterized by

(■ ■ • n, . . . ; a) (4)

Here ni are the occupation num-
bers of the radiation oscillators
(the numbers of photons present
in each oscillator /) and a indi-
cates the stationary state of the
atom.

The states 4 are no longer sta-
tionary when the perturbation en-
ergy /Y1 is taken into account. The
theory yields simply and directly
the laws of emission and absorp-
tion of light. Indeed, the state
(. . . 0,0, . . . \a) of an atom in an
excited state a without any radi-
ation present is not stationary ac-
cording to the Hamiltonian 3. A
first-order perturbation calculation
gives a probability Pabdfl per unit
time for a transition from a to a
lower state b, accompanied by the
emission of a photon of a frequen-
cy co = (ea - eb)//i into the solid
angle dfl and with a polarization
vector s:

Pabdn = /0|sjat, \2dO (5)

nc fico*

l0 is given by the expression 1 .

The matrix element is determined
by (for a one-electron system)

Lb = j j exp(/ kabx)if>bdx 3

where j is the operator of the cur-
rent, and Wab the wave vector of
the emitted quantum. The effect
of the size of the system com-
pared to the wavelength is taken
into account by the exponential; it
was neglected in the oscillator pic-
ture (dipole approximation). Ac-
cording to equation 5 spontaneous
emission appears as a forced
emission caused by the zero-point
oscillations of the electromagnetic
field, which are always present,

even in a space without any pho-
tons.

This was the start of an interest-
ing development in theoretical
physics. After Einstein had put an
end to the concept of aether, the
field-free and matter-free vacuum
was considered as a truly “empty
space.” The introduction of quan-
tum mechanics changed this situa-
tion and the vacuum gradually be-
came “populated.” In quantum
mechanics an oscillator cannot be
exactly at its rest position except
at the expense of an infinite mo-
mentum, according to Heisen-
berg’s uncertainty relation. The
oscillatory nature of the radiation
field therefore requires zero-point
oscillations of the electromagnetic
fields in the vacuum state, which is
the state of lowest energy. The
spontaneous emission process
can be interpreted as a conse-
quence of these oscillations.

Dirac’s theory produced all re-
sults regarding the absorption and
emission of light by atoms that
previously were obtained by unre-
liable arguments. The results fol-
lowed from the Hamiltonian 3
when the interaction energy 2 was
treated as a first-order perturba-
tion. Some other radiation phe-
nomena such as photon scattering
processes, resonance fluores-
cence and nonrelativistic Compton
scattering of photons by electrons,
appear in the second order of the
perturbation treatment. The the-
ory gave excellent account of all
radiation phenomena in that order
of perturbation in which they first
appear. The higher approxima-
tions give rise to difficulties, which
will be discussed later on.

Coupling to
relativistic systems

In 1928 Dirac published two pa-
pers on a new relativistic wave
equation of the electron. It was
his third great contribution to the
foundations of physics; the first
was the reformulation of quantum
mechanics, the “transformation
theory,”2 the second was the the-
ory of radiation. The Dirac equa-
tion was supposed to replace
Schrodinger’s equation for cases
where electron energies and mo-
menta are too high for a nonrelati-
vistic treatment. It immediately
gave rise to four great triumphs:

► The spin fi/2 of the electron ap-
peared to be a natural conse-
quence of the relativistic wave
equation. (It turned out later that
there exist relativistic wave equa-
tions for particles with different
spin. Dirac’s equation for a spin
fi/2 is distinguished by the fact
that the energy operator appears
linearly.)

► The ^-factor of the electron
necessarily has the value g = 2.
The value of the magnetic mo-
ment of the electron followed di-
rectly from the equation.

► When applied to the hydrogen
atom, the equation yields the cor-
rect Sommerfeld formula for the
fine structure of the hydrogen
spectrum.

The coupling of the quantized
radiation field with the Dirac equa-
tion made it possible to calculate
the interaction of light with relativ-
istic electrons. The most impor-
tant results were the derivation of
the Klein-Nishina formula for the
scattering of light by electrons, the
Mdller formula for the scattering of
two relativistic electrons, and the
emission of photons when elec-
trons are scattered by the Cou-
lomb field of nuclei.

In spite of these amazing suc-
cesses a number of serious diffi-
culties turned up immediately and
it took a long time to solve them.
The difficulties came from the ex-
istence of states of negative kinet-
ic energy or negative mass. There
was no way to get rid of them. If
one tried to exclude them from the
Hilbert space of the electron, the
space becomes incomplete; fur-
thermore, the Klein-Nishina formu-
la could not be derived without
them. Taken at face value, the
existence of those states would
imply that the hydrogen atom is
not stable because of radiative
transitions from the ordinary states
to the states of negative energy.
The properties of those impossible
states were constantly in the cen-
ter of discussion during those
years. George Gamow referred to
electrons in these states as “don-
key electrons” because they tend
to move in the opposite direction
to the applied force.

Triumph and curse
of the filled vacuum

It was again Dirac who pro-
posed a way out of the difficulty in

PARTICLES AND QUANTA

361

1929. As it happens with ideas of
great men, it was not only “a way
out of a difficulty” but it was a
seminal idea that led to the recog-
nition of the existence of antimat-
ter and ultimately to the develop-
ment of field theory with all its
concomitant insights into the na-
ture of matter. He made use of
the Pauli principle and assumed
that, in the vacuum, all states of
negative kinetic energy are occu-
pied. This was the second step in
the development of “populating”
the vacuum. Later on this step
was somewhat mitigated by elimi-
nating the notion of an actual
presence of those electrons, but
the fluctuations of matter density
in the vacuum remained as an ad-
ditional property of the vacuum be-
sides the electromagnetic vacuum
fluctuations.

Dirac’s daring assumption had
most disturbing consequences,
such as an infinite charge density
and infinite (negative) energy den-
sity of the vacuum. Some of
these impossible consequences
were circumvented later, as is re-
ported in the next section. How-
ever, the assumption not only
solved most of the problems of
the negative energy states but led
to an impressive and unexpected
broadening of our views about
matter.

First of all, the transitions from
positive to negative energy states
were excluded, and the stability of
the atoms was assured. Further-
more, Dirac’s assumption required
the existence of processes in
which one particle from the “sea”
of filled negative states is lifted to
a state of positive energy, if the
necessary energy is supplied by
absorption of photons or by other
means. A hole in the sea and a
normal particle would be created.
The hole would have all the prop-
erties of a particle of opposite
charge. Moreover, a particle
could fall back into a hole with the
emission of photons of the right
amount of energy and momen-
tum. This, of course, would be a
process of particle-antiparticle
annihilation. Thus Dirac’s as-
sumption led to the recognition of
the existence of antiparticles and
of the existence of two new funda-
mental processes: pair creation
and annihilation.

In the beginning these ideas
seemed incredible and unnatural
to everybody. No positive elec-
tron was ever seen at that time;
the asymmetry of charges, positive

for the heavy nuclei, negative for
the light electrons, seemed to be a
basic property of matter. Even
Dirac shrank away from the con-
cept of antimatter and tried to in-
terpret the positive “holes” in the
sea of the vacuum electrons as
being protons. It was soon recog-
nized, however, by Hermann Weyl,
Robert Oppenheimer and by Dirac
himself, that this interpretation
would again lead to an unstable
hydrogen atom and that the holes
must have the same mass as the
particles. Antimatter ought to ex-
ist. Indeed the positron was
found by Carl Anderson in 1932;
the antiproton was discovered 25
years later because its production
needed energy concentrations
several thousand times higher
than were available before the in-
vention of the synchrocyclotron.
(The possibility of antiparticles was
already mentioned by Pauli3 and
Einstein.4 More about this can be
found in a review by A. Pais.5)

Once the idea of the filled vacu-
um took hold, it was relatively
easy to calculate the cross section
for the annihilation of an electron
and a positron into two photons
and the cross section for pair cre-
ation by photons in the Coulomb
field of atomic nuclei. It is aston-
ishing that it took more than three
years after the identification of the
holes with positrons, before the
pair creation in a Coulomb field
was calculated, although it was a
very simple determination of a
transition probability. It illustrates
the wonder and incredulity that
those ideas encountered during
the first years.

Today it is hard to realize the
excitement, the skepticism and the
enthusiasm aroused in the early
years by the development of all
the new insights that emerged
from the Dirac equation. A great
deal more was hidden in the Dirac
equation than the author had ex-
pected when he wrote it down in
1928. Dirac himself remarked in
one of his talks that his equation
was more intelligent than its au-
thor. But it was Dirac who found
most of the additional insights him-
self.

The formulas derived for the
creation of pairs and for radiative
scattering (Bremsstrahlung) also
gave an excellent account of the
development of cosmic-ray cas-
cade showers in matter, once the
incoming energy is transformed
into electrons and photons. It is
interesting to observe how this

success was interpreted. First it
was considered as proof that radi-
ation theory and pair creation are
valid even at very high energy.
Then, when it turned out that a
part of the cosmic rays do not
form showers (the part consisting
of the then-unknown muons),
doubts were expressed as to the
validity of radiation theory at high
energies. But it was shown by
Enrico Fermi6 and then by C. F.
Von Weizsacker7 and E. J. Wil-
liams8 that the effect of a Cou-
lomb field on a fast-moving elec-
tron can be expressed as the
effect of light quanta whose ener-
gy is only a few me2, when a suit-
able system of reference was
used (the system in which the
electron is at rest). This analysis
of the production of cascade
showers showed clearly that only
energies and momenta of the or-
der me2 and me are exchanged in
the relevant processes. Hence
the shower production does not
test the theory at high energies,
nor could any deviation from the
expected showers be explained by
a breakdown of the theory at high
energies.

Indeed, electron accelerators of
many GeV were needed to test
the theory at large energies. Re-
cent measurements with electron-
positron colliders have shown radi-
ation theory to be valid at least up
to energy exchanges of 100 GeV.

How unreasonable the idea of
antimatter seemed at that time
may be illustrated by the fact that
many of us did not believe in the
existence of an antiparticle to the
proton because of its anomalous
magnetic moment. The latter was
measured by Otto Stern in 1 933
and could be interpreted as an in-
dication that the proton does not
obey the Dirac equation. The fun-
damental character of the matter-
antimatter symmetry and its inde-
pendence of the special wave
equations was recognized only
very slowly by most physicists.

The following conclusions must
be drawn from the new interpreta-
tion of the negative-energy states
in the Dirac equation. There are
no real one-particle systems in
Nature, not even few-particle sys-
tems. Only in nonrelativistic quan-
tum mechanics are we justified to
consider the hydrogen atom as a
two-particle system; not so in the
relativistic case, because we must
include the presence of an infinite
number of vacuum electrons. Even
if we consider the filled vacuum as

362

HISTORY OF PHYSICS

a clumsy description of reality, the
existence of virtual pairs and of
pair fluctuations shows that the
days of fixed particle numbers are
over.

Furthermore, relativity requires
that time and space be treated
equivalently. In nonrelativistic
quantum mechanics, time is a
parameter, whereas the space co-
ordinates of the particles are con-
sidered as operators. In relativis-
tic quantum mechanics the
particles appear as quanta of a
field, just as the photons are quan-
ta of the electromagnetic one. The
fields assume the role of operators
and the coordinates are param-
eters indicating the space- or time-
dependence of the field opera-
tors. The theory of the interaction
of charged particles with the radi-
ation field becomes a field theory
in which two (or more) quantized
fields interact: the matter field
and the radiation field.

The field amplitudes are ex-
pressed as linear combinations of
creation and destruction operators
that increase or decrease the
number of particles in the quantum
states of the system. It is a direct
generalization of the quantization
of the electromagnetic field as de-
composed into oscillator ampli-
tudes. The operator of an oscilla-
tor amplitude contains matrix
elements only between states that
differ by one unit of excitation. The
corresponding operator either
adds (creates) or subtracts (de-
stroys) a quantum of the oscillator.

There are essential differences
between a field of particles with
spin V2 and the radiation field. The
former describes the behavior of

Discovery of the positron.

Cloud chamber photo by Cart
Anderson in 1931 showing the
first recorded positron track.

fermions, whereas the latter is an
example of a boson field. In the
classical limit, the boson fields are
classical fields whose field
strength is a well-defined function
of space and time (radio wave).
The fermion fields cannot have a
classical limit because no more
than one fermion can be put into
one wave; its classical limit is a
particle with a well-defined mo-
mentum and position. So far, the
constituents of matter have all
been shown to be fermions inter-
acting by means of boson fields.

Furthermore, the interaction be-
tween fermion and boson fields in
its simplest form necessarily is bi-
linear in the fermion fields and lin-
ear in the boson fields. This is in-
dicated by the fact that the current
density is a bilinear expression of
the particle wave functions. One
cannot construct a Lorentz-invar-
iant expression that is linear or cu-
bic in the spinor wave functions.
Boson field (vector or scalar),
however, may appear linearly in
the interaction.

When the fields are expressed
in terms of creation and annihila-
tion operators, the form of the in-
teraction can be interpreted in the
following way: The fundamental
interaction between fermions and
bosons consists of the product of

James Clerk Maxwell

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PARTICLES AND QUANTA

363

two fermion creation or destruction
operators bf and b , and one bo-
son operator a or a +: b 1 ba or
b fba f. It is interpreted as a
change of state of a fermion “de-
stroyed” in one state and “cre-
ated” in another) accompanied
with either an emission or an ab-
sorption of a boson.

The fight against
infinities: elimination of
the vacuum electrons

In spite of all successes of the
hole theory of the positron, the in-
finite charge density and the infi-
nite negative energy density of the
vacuum made it very difficult to ac-
cept the theory at its face value. A
war against infinities started at that
time. It was waged with increas-
ing fervor by the developers of
quantum electrodynamics when
more intricate infinities appeared
besides those mentioned before,
as will be described in the subse-
quent sections.

There is a rather primitive way
to take care of the infinite charge
density, by a slight change in the
definition of charge and current. It
amounts to the following argu-
ment: Because the theory is com-
pletely symmetric in regard to
electrons and positrons, it would
be equally valid to construct a the-
ory in which the positrons are the
particles and the electrons are the
holes in a sea of positrons that oc-
cupy negative energy states. The
actual theory then could be con-
sidered as a superposition of
these two theories, one with an in-
finite negative charge density and
the other with infinite positive
one. This combination also
serves to emphasize the symmetry
between matter and antimatter.

The vacuum charge densities can-
cel; the corresponding expres-
sions for charge and current in-
deed give a more satisfactory
description of the phenomena.

It was recognized in 1934 by
Heisenberg9 and by Oppenheimer
and Wendell Furry 10 that the cre-
ation and destruction operators
are most suitable for turning the li-
ability of the negative energy
states into an asset, by inter-
changing the role of creation and
destruction of those operators that
act upon the negative states. This
interchange can be done in a con-
sistent way without any fundamen-
tal change of the equations. The
consequences are identical to

those of the filled-vacuum as-
sumption, but it is not necessary
to introduce that disagreeable as-
sumption explicitly. Particles and
antiparticles enter symmetrically
into the formalism, and the infinite
charge density of the vacuum dis-
appears. One even can get rid of
the infinite negative-energy density
by a suitable rearrangement of the
bilinear terms of the creation and
destruction operators in the Hamil-
tonian. After all, in a relativistic
theory the vacuum must have van-
ishing energy and momentum.
There remains, however, the un-
pleasant fact of the existence of
vacuum fluctuations without any
energy.

The fundamental interaction be-
tween charged fermions and pho-
tons now contains three basic pro-
cesses: the scattering of a
fermion with the emission or ab-
sorption of a photon, the creation
and the annihilation of a fermion-
antifermion pair with the emission
or absorption of a photon. All
electrodynamic interaction pro-
cesses are combinations of these
fundamental steps.

Surprisingly enough, it took
many years before the physicists
realized the great advantages of
this new formalism. One still
reads about the “hole theory” of
positrons in papers written in the
late 1940s, when renormalization
was the topic of the day.

An interesting episode in the
fight for the elimination of vacuum
electrons was the quantization of
the Klein-Gordon relativistic wave
equation for scalar particles. It
seemed to be a rather academic
activity because no scalar particle
was known at that time. In that
theory, the charge density
(4 )*<b — i/><f>*) and the wave intensity
\<f>\2 are not identical. Therefore,
it seemed posssible that, under
the influence of external electro-
magnetic fields, the total intensity
$\<t>\2dx 3 may change in time, al-
though the total charge remains
conserved. It smelled of a cre-
ation or annihilation process of op-
positely charged particles. The
problem attracted the attention of
Pauli and myself11 because we
saw that the quantized Klein-Gor-
don equation gives rise to particles
and antiparticles and to pair cre-
ation and annihilation processes
without introducing a vacuum full
of particles. Note that at the time
the method of exchanging the cre-
ation and destruction operators
(for negative energy states) was

not yet in fashion; the hole theory
of the filled vacuum was still the
accepted way of dealing with posi-
trons. Pauli called our work the
“anti-Dirac paper;” he considered
it as a weapon in the fight against
the filled vacuum, which he never
liked. We thought that this theory
only served the purpose of an un-
realistic example of a theory that
contained all the advantages of
the hole theory without the neces-
sity of filling the vacuum. We had
no idea that the world of particles
would abound with spin-zero enti-
ties a quarter of a century later.
This was the reason why we pub-
lished it in the venerable but not
widely read Helvetica Physica
Acta.

Our work on the quantization of
the Klein-Gordon equation led
Pauli to formulate the famous rela-
tion between spin and statistics.
Pauli demonstrated in 1936 the
impossibility of quantizing equa-
tions of scalar or vector fields that
obey anticommutation rules. He
showed that such relations would
have the consequence that phys-
ical operators do not commute at
two points that differ by a space-
like interval. This lack of commu-
tativity would contradict causality
because it would require that mea-

Hideki Yukawa

364

HISTORY OF PHYSICS

surements interfere with each oth-
er when no signal can pass from
one to the other. Thus Pauli con-
cluded that particles with integer
spin cannot obey Fermi statistics.
They must be bosons. During the
days of the hole theory it was ob-
vious that particles with spin Y2
cannot obey Bose statistics be-
cause it would be impossible to
“fill” the vacuum. Four years lat-
er Pauli proved the necessity of
Fermi statistics for half-integer
spins, also on the basis of the
same causality arguments.

The fight
against infinities:
infinite self mass

The infinities of the filled vacu-
um and of the zero-point energy of
the vacuum turned out to be rela-

Wolfgang Pauli in 1931

AIP NIELS BOHR LIBRARY

tively harmless compared to other
infinities that appeared in quantum
electrodynamics when the cou-
pling between the charged parti-
cles and the radiation field was
considered in detail. No difficul-
ties appeared as long as only the
first terms of the perturbation
treatment were taken into account,
that is those terms in which the
phenomena under consideration
appear in the lowest order. It
soon turned out that the higher
terms always contain infinities, as
Oppenheimer12 had pointed out
for the first time.

In 1934 Pauli asked me to cal-
culate the self energy of an elec-
tron according to the positron the-
ory. It was a modern repetition of
an old problem of electrodynam-
ics. In classical theory the energy
contained in the field of an elec-
tron of radius a (neglecting the in-
side) is 4 ve2/a and would diverge
linearly if the radius goes to zero.
The corresponding calculation in
the positron theory is much more
complicated. One had to calcu-
late the difference between two in-
finite amounts: the energy of the
vacuum and the energy of the
vacuum plus one electron. The
result was equivalent to the state-
ment that the electric field inside
one Compton wave length
Ac = h/mc from the electron is not
e/r2 but (e/i2)(r/Ac)'[/2. When r
goes to zero it increases only as
r 3/2. The self energy then be-
comes12

E = m0c2 + (3/2ir)m0c2

X(e2/fic)\og(A.c/a) (6)

where m0 is the intrinsic or “me-
chanical” mass of the electron,
which appears in the Hamiltonian
of the electron when it is decou-
pled from the electromagnetic
field. It diverges only logarithmi-
cally.

(This brings back one of the
dark moments of my professional
career. I made a mistake in the
first publication that resulted in a
quadratic divergence of the self-
energy. Then I received a letter
from Furry, who kindly pointed out
my rather silly mistake and the
fact that actually the divergence is
logarithmic. Instead of publishing
the result himself, he allowed me
to publish a correction quoting his
intervention. Since then the dis-
covery of the logarithmic diver-
gence of the electron self-energy
is wrongly ascribed to me instead
of to Furry.)

A consistent relativistic theory

requires a point electron, that is
a — ► 0. It is worth noting, howev-
er, that the value of a for which
the second term of 6 becomes
half of the first is as small as
10_72cm! Even the Schwarzs-
child radius of the electron is only
10_55cm. This value means that
the deformation of the space
around the electron is strong
enough to prevent the electron
from interacting with photons of
that wave length, thus providing a
natural cut-off long before the
electromagnetic self-energy be-
comes important. Unfortunately,
no consistent calculation of this
effect has ever succeeded.

Another somewhat more benign
type of infinities appeared in quan-
tum electrodynamics when emis-
sions of photons of very low fre-
quencies were considered. Such
emissions take place, for example,
when electron beams are scat-
tered by static electric fields. Clas-
sical theory predicts that the emit-
ted energy does not vanish in the
limit of zero frequencies. The
quantum result ought to be identi-
cal with the classical one at that
limit; it would indicate that the
number of emitted quanta goes to
infinity. This trouble, called “in-
frared catastrophe,” can be avoid-
ed by describing this limit with the
help of classical fields, as Bloch
and Arnold Nordsieck14 have
shown in their important paper of
1937. It put an end to any worries
about this kind of infinity.

The fight against
infinities: infinite
vacuum polarization

The virtual pairs endow the
vacuum with properties similar to a
dielectric medium. We may as-
cribe a dielectric coefficient e to
the vacuum. A direct calculation
of this dielectric effect leads to a
dielectric coefficient that consists
of a constant part e0 and an addi-
tional part that depends upon the
electromagnetic fields and their
derivatives in time and space.

e = e0 + e(field) (7)

The constant part e0 cannot have
any physical significance because
it serves only to redefine the unit
of charge. Any charge O0 would
appear as 0 = Oo/e. The actual
value of e0 turns out to be logarith-
mically divergent (it goes as
\og(A/m) where A is the highest
momentum considered in the cal-

PARTICLES AND QUANTA

365

culation). The additional field-de-
pendent term, however, turns out
to be finite and therefore should
have physical significance.

Let us now consider what hap-
pens to a charge O0 when placed
in a vacuum with a dielectric coef-
ficient of the form 7. At large dis-
tances r the effective charge will
be Qq/cq. When r becomes of the
order Ac = fi/(mc) or less the sec-
ond term of 7 becomes impor-
tant. Calculations of this term for
a Coulomb field were carried out
by Robert Serber15 and E. Uehl-
ing.16 They found that e{r) de-
creases with r when r becomes
smaller than the Compton wave
length Ac . This is so because, for
smaller r, only those virtual pairs
contribute whose energy is larger
than fic/r. This decrease is finite
and calculable. The infinite value
of e0 was interpreted as an indica-
tion that the intrinsic “true” charge
O0 is infinite so that the observed
charge becomes finite and equal
to e = Q0/e0 for r—> <x . The de-
crease of e with decreasing r when
r<Ac would then amount to an in-
crease of the effective charge Oe„
at those small distances.

This increase of Qe„ for r<Ac
over the value e at large distances
is rather small; it is of the order of
e/1 37. A strong increase occurs
only at very small distances
r~Ac exp( — fic/e2)] these are the
same distances as the ones we
discussed in connection with the
self-energy, at which the theory
most likely is inapplicable. We
then get a dependence of Oefi on
the distance as shown in figure 2.

It is the first example of a “running
coupling constant,” which plays an
important role in quantum chromo-
dynamics.

The fight
against infinities:
renormalization

The appearance of infinite mag-
nitudes in quantum electrodynam-
ics was noticed in 1 930. Because
they only occurred when a certain
phenomenon was calculated to a
higher order of perturbation theory
than the lowest one in which it ap-
peared, it was possible to ignore
the infinities and stick to the low-
est-order results that were good
enough for the experimental accu-
racy at that period. However, the
infinities at higher order indicated
that the formalism contained unre-
alistic contributions from the inter-

Running coupling constant in

QED. The effective charge
Qa„ as a function of the
distance r. The distance a, the
distance at which Qe„ is about
137 e, is very much smaller
than indicated in this
drawing. Figure 2

Willis Lamb in 1947

® NEWSWEEK REPRINTED 8V PERMISSION.

366

HISTORY OF PHYSICS

Julian Schwinger

Richard Feynman (photo by
Sylvia Posner, courtesy of the
CalTech Archives)

action with high-momentum pho-
tons.

Already in 1936 the conjecture
was expressed1718 that the infinite
contributions of the high-momen-
tum photons are all connected
with the. infinite self mass, the infi-
nite intrinsic charge Q0 and with
nonmeasurable vacuum quantities
such as a constant dielectric coef-
ficient of the vacuum. Thus it
seemed that a systematic theory
could be developed in which these
infinities are circumvented. At
that time nobody attempted to for-
mulate such a theory, although it
would have been possible then to
develop what is now known as the
method of renormalization.

There was one tragic exception
and that was E. C. G. Stueckel-
berg.19 20 He wrote several im-
portant papers in 1 934-38, putting
forward a manifestly invariant for-
mulation of field theory. This
could have been a basis of devel-
oping the ideas of renormaliza-
tion. Later on (in 1947) he actual-
ly formulated the complete
renormalization procedure quite in-
dependently of the efforts of other
authors. Unfortunately, his writ-
ings and his talks were rather ob-
scure and it was very difficult to
understand them or to make use
of his methods. Had the theorists
been capable of grasping his ideas
they may well have calculated the
Lamb shift and the correction to
the magnetic moment of the elec-
tron at a much earlier time.

A new impetus to such attempts
came from an experimental re-
sult. Willis Lamb and R. C. Reth-
erford21 were able to measure reli-
ably the difference in energy
between the 2S1/2 and 2P1/2 state
of hydrogen (Lamb shift). The
two states should have been ex-
actly degenerate according to the
Dirac equation applied to the hy-
drogen problem. Already in the
1930s the degeneracy of these
two levels was in doubt from spec-
troscopic measurements, but
Lamb and Retherford, using newly
developed microwave methods,
definitely established the splitting
and measured it with great preci-
sion.

It had been conjectured long
ago that such a splitting should be
caused by the coupling of the radi-
ation field with the atom, but early
attempts to calculate it ran into dif-
ficulties because the infinite mass
and vacuum polarization appeared
in the same approximation. It was

PARTICLES AND QUANTA

367

H. A. Kramers who pointed out22
that one ought to be able to calcu-
late the effect by carefully sub-
tracting the infinite energy of the
bound electron from that of the
free one and thereby separating
the parts that contribute to the
mass and charge from those of
real significance. Infinities are al-
ways difficult to subtract in an un-
ambiguous way. After the Lamb
shift had been measured, Bethe
had made an attempt to estimate
the effect of the radiation coupling,
simply by omitting the coupling
with photons of an energy larger
than me2. This attempt was suc-
cessful because most of the effect
comes from the coupling with pho-
tons of lower energy, which can
be treated nonrelativistically.

An exact calculation to the low-
est order in (e2/fic) was then per-
formed by Norman M. Kroll and
Lamb23 and by J. B. French and
myself24 (1949) and resulted in
good agreement with the experi-
ment. However, the methods
used by those authors of subtract-
ing two infinities were clumsy and
unreliable. Subsequently, a formi-
dable group of physicists, includ-
ing Julian Schwinger, Richard
Feynman, Freeman Dyson and
Sin-ltiro Tomonaga, developed a
reliable way to deal with the infin-
ities. They introduced a method
of renormalization in which the ini-
tial parameters were eliminated in
favor of those with immediate
physical significance. In any com-
putation of an electrodynamical re-
sult, the effects of the mass and
charge redefinitions had to be in-
corporated. Infinite “counter-
terms” are introduced into the Ha-
miltonian in such a manner that
they compensate for the infinite
mass and charge. In order to
make this procedure unambiguous
it was necessary to keep the ex-
pressions in a manifestly relativis-
tic and gauge-invariant form
throughout the calculations.

The results were most encour-
aging. Schwinger found that the
magnetic moment of the electron
should indeed be larger by the fac-
tor 1 + a/(2ir) than the Bohr mag-
neton, a result that was observed
shortly before by I. I Rabi and his
disciples and then more accurately
by Henry Foley and Polykarp
Kusch. The Lamb-shift results
were recalculated in a much
simpler way, radiative corrections
of higher order in e2/fic to scatter-
ing processes were unambiguous-

ly determined, and the vacuum po-
larization effects were worked out
in detail; the latter found an im-
pressive experimental confirmation
in the measurements of the spec-
trum of muonic atoms (the elec-
tron replaced by a muon); the
muon moves in the region
r~{fi/mec ) where the vacuum po-
larization is a one-percent effect.

Another remarkable test of the
new methods was the agreement
between the predicted and ob-
served properties of positronium—
the atom consisting of an electron
and a positron, discovered and in-
vestigated for the first time by
Martin Deutsch.

The war against infinities was
ended. There was no reason any
more to fear the higher-order
terms. The renormalization took
care of all infinities and provides
an unambiguous way to calculate
with any desired accuracy any
phenomenon resulting from the
coupling of electrons with the
electromagnetic field. It was not a
complete victory, because infinite
counter-terms had to be intro-
duced to remove the infinities.

Furthermore, the procedure of
eliminating infinities could be car-
ried out only by renormalizing
successively at each step of the perturbation expansion in powers of the
coupling parameter. It still is not clear whether this method leads to a
convergent series. It is like Hercules’s fight against Hydra, the many-
headed sea monster, which grows a new head for every one cut off.

But Hercules won his fight and so did the physicists. Sidney Drell char-
acterized the situation most aptly as “a peaceful coexistence with the
infinities.”

Here are the signs of victory in the war against infinities:

► Lamb shift (about 10% is due to vacuum polarization; most of the
rest is the interaction with the zero-point oscillations of the electromag-
netic field):

Sin-ltiro Tomonaga

Av(2S1/2 — 2P 1/2)

1057.862 (20) MHz (exp.)
1057.864 (14) MHz (theor.)

► p-factor of the electron (a = Vz(g — 2)) x 1 03

_ 1 .1 5965241 (20) (exp.)
a~ 1.159652379 (261) (theor.)

► Vacuum polarization. 90% of the Lamb shift in muonic helium (a
particle + muon) is caused by vacuum polarization:

AE( 2Si/2 — 2P 3/2) —

1.5274 (0.9) eV (exp.)
1.5251 (9) eV (theor.)

In spite of these victories there remain nagging problems in quantum
electrodynamics. There are definite indications that we understand only
a partial aspect of what is going on. As was mentioned before, the
elimination of infinities is possible only in a perturbation approach; it is
contingent upon the smallness of e2/hc. But the effective coupling
constant at very small (indeed incredibly small) distances becomes larg-
er than unity. Will there be a theory that avoids renormalization by us-
ing nonperturbative methods? Or will a future unification of electrody-

368

HISTORY OF PHYSICS

E. B. BOATNER

Steven Weinberg

namics and general relativity heal
the disease of divergencies be-
cause of the fact that the danger-
ous distances are smaller than the
Schwarzschild radius of the elec-
tron?

Moreover, there is no way to un-
derstand and derive the mass of
the electron within today’s electro-
dynamics. This problem has be-
come even more acute since hea-
vier electrons such as the muon
and the r-electron have been dis-
covered. There is not the slight-
est indication why electrons with
different masses should exist. In
present-day field theories the
masses are arbitrary parameters
that may assume any values.

Abdus Saiam

E. B. BOATNER

Sheldon L. Glashow

Quantum electro-weak
dynamics

The tremendous quantitative
success of renormalized quantum
electrodynamics (QED) has elevat-
ed this theory as an (almost) spot-
less example of a physical theory
dealing with the interactions of
electrically charged particles with
fields. No wonder that the physi-
cists tried to apply similar methods
whenever interactions between
fermions and bosons occurred.

The first well-known use of QED
as an example was the attempt of
Hideki Yukawa (1935) to describe
the nuclear force between protons
and neutrons as an emission and
subsequent absorption of a virtual
boson. He had to ascribe a mass
to that boson, because the nuclear
force has a short range r0 of the
order of 10-13 cm. Any field the-
ory modelled after QED would give
an exponential force between fer-
mions of the form r~ 1 e ~
with M the mass of the boson.

The observed range of nuclear
forces leads to a mass of about
200 MeV. No such bosons were
known at that time, but he predict-
ed the existence of them. His
prediction was confirmed ten
years later — an impressive suc-
cess of a simple idea. Actually the
nuclear force turned out to be the
effect of somewhat more compli-
cated processes; it does not de-
tract from the beauty of his predic-
tion.

The second early attempt to use
QED as an example is a little
known contribution by Oskar
Klein.25 He suggested a model
for the weak interactions in which
massive charged vector bosons
mediated processes such as /? de-

cay. He even called them by the
currently used letter W. He was
the first to propose that the neu-
tron decay: n— .-p + e + vbe split
into two consecutive steps:

n-*p + W W“— e + T (8)

He even went as far as to assume
that the coupling constant for such
processes is e2/fic, the same as
for electromagnetic events. He
attributed the smallness and the
short range of the weak interac-
tions to a large mass of the W, as
it is done today, and he arrives at
a W mass of about 1 00 GeV. This
was 20 years before Schwinger in-
dependently took up this idea
again. Schwinger initiated a de-
velopment that brought forward
the present unified quantum elec-
tro-weak dynamics, referred to as
QEWD, a development in which a
large number of theorists took
part, including Martinus Veltman,
Gerard ‘t Hooft, P. W. Higgs, R.
Brout, Sheldon Glashow, Steven
Weinberg, Benjamin W. Lee and
Abdus Saiam. An excellent his-
torical survey has been written by
Sidney Coleman.26

Before entering the discussion
of those new ideas it is necessary
to modernize the relations 8. We
assume today that the proton and
the neutron are not elementary but
are made up of three quarks, the
proton being the combination uud,
the neutron ddu. Here u and d
stand for the two most important
quark types; u carries the charge
% e and d carries - % e. They
represent an isotopic doublet.

Thus the transitions 8 and their in-
verse are pictured today as transi-
tions between the two doublet
states:

d->u + W~

/ e + ve

W“— /i + vM 0)

\ T + VT
/ e + ve

W+— ►jS +

\r + vT

The bar denotes the antiparticle.
(There is a refinement that we will
not treat in any detail. In the fun-
damental weak interaction process
d is replaced by a linear combina-
tion d' = ad + bs, where s is the
so-called strange quark. This re-
finement allows a weak transition
in which the strangeness
changes. These effects are
smaller than 9 because b<a.
Similar mixtures between quark
types in weak interactions appear

PARTICLES AND QUANTA

369

between the higher quark types.)

C. N. Yang and R. L. Mills27 pro-
vided the key idea that was neces-
sary in order to apply field theory
to weak and later to strong inter-
actions. It is a generalization of
the field concept that underlies
QED. In the latter the source of
the field is a scalar magnitude, the
charge of the particles. The field
does not carry any charge; the
charge always stays with the parti-
cles. Such theories are called
“abelian” theories. Nonabelian
field theories, as the ones intro-
duced by Yang and Mills, contain
two new features:

► The source of the field is not a
scalar charge, but an internal
quantum number of the source
particle, for example a spinor
charge, such as the isotopic-spin
quantum number (called “up” or
“down” in the case of proton and
neutron).

► The source particle can ex-
change its “charge” (the isospin)
with the field in the interaction pro-
cess.

In such theories the field itself
carries charge and, therefore, acts
as a source of fields; there is a di-
rect interaction process between
field quanta. Whereas the funda-
mental diagram of QED is the cou-
pling of the charged particle with
the field (see figure 3a) the non-
abelian theories also contain an-
other fundamental diagram denot-
ing the coupling between field
quanta. The mathematical formu-
lation of nonabelian field theories
is based upon a generalization of
gauge invariance; we will not enter
here into these formal, though es-
sential, arguments, except by not-
ing that they require the field
quanta to be massless vector bo-
sons.

To come closer to an under-
standing of the present view re-
garding electro-weak dynamics,
we start by discussing the theory
at very high energies, much higher
than the mass of the W, that is
much higher than 100 GeV. In
that region the weak interactions
and the electric interactions are
neatly separated. Let us first dis-
cuss the former ones. We intro-
duce the so-called weak isodoub-
lets, consisting of the u-d quark
pair (actually u — d'; see paren-
thetical remark on page 80), and
the three neutrino-electron pairs:

Doublet (left-handed) u ve vT

d e p t

Hypercharge V' V V V

Only the left-handed particles form
these isodoublets. The right-
handed ones have no weak inter-
actions. These doublets emit or
absorb three types of bosons ac-
cording to the scheme:

a+±b + W+
b +± a + W~

a a + W°
b b + W°

(10)

Here a — b stands for any iso-
doublet of the table above; the
coupling constant for each pro-
cess is g. The process corre-
sponds to the diagram of figure 3a
with a coupling constant g. The
basic gauge invariance of this for-
malism requires that the three pro-
cesses 8 have the same probabil-
ities and that the three W’s are
massless vector bosons.

In addition to the “SU(2)-type”
couplings of equation 10 we also
introduce a “hyper-electromagnet-
ic” coupling. It is analogous to
the ordinary electromagnetic one
(“U(1 ) coupling”), but the two
members a and b carry the same
scalar “hypercharge” 77' or 77, de-
pending on whether we consider
the quark pair or the lepton pairs.
This coupling does not distinguish
right- and left-handed particles; it
applies to both. We therefore get
the processes (with coupling con-
stants 77' or 77)

a +± a + B°

b b + B°

(11)

where B° is the massless quantum
(vector boson) of the hyper-elec-
tromagnetic field. At very high en-
ergies we then expect the quarks
and leptons to be coupled to the
W field in a nonabelian way be-
cause, according to equation 10
the iso-spinor charges are trans-
ferred to the field and vice versa;
but they are coupled to the B field
in an abelian way via the scalar
hypercharge 77 or 77'.

This picture can be right only at
very high energies. The mass of
the W would show up at a lower
energy. We also find there that
the electromagnetic field is coup-
led to different charges in each
isodoublet. How does Nature
achieve these deviations from the
symmetric theory at high ener-
gies? The current theories postu-
late something that is called
“spontaneous symmetry breaking”
at lower energies. It is caused by
a new isotopic spinor field— the
Higgs field. It has the following
remarkable property: Its energy is

such that it has a minimum not
when the field is zero but when it
has a finite value given by the
spinor j^o,0j. That would mean
that the vacuum has a certain
fixed direction in isospace, namely
the direction of the spinor <j>Q. At
high energy this is no longer true
because there the energy gained
by choosing <j>0 instead of zero is
negligible. The situation is like
that of a ferromagnet, in which a
direction in real space is deter-
mined as long as the energy trans-
fers are smaller than the Curie en-
ergy. Thus at low energies the
Higgs field destroys the symmetric
situation described before. The
effects of this destruction by the
finite expectation value of the
Higgs field are as follows:

► The hyper-electromagnetic field
B and the W° field get mixed by
an arbitrary mixing angle <9W ,
called the Weinberg angle. The
two emerging linear combinations
are

Z = cos<9w W° + sin<9w B n 0,

A = - sin<9w W° + cos<9w B

► The Higgs field is coupled with
the other field in such a way that
W+ and W~ acquire a mass

Z gets a different mass Mz ,
whereas the field A remains mass-
less and becomes the electromag-
netic field (photons).

► The fact that W+ and Z have
large masses reduces the weak in-
teraction effects compared to the
electric ones, at low energies.

► The coupling of the quarks and
leptons to the electromagnetic
field A is different from the cou-
pling to the hyper-electromagnetic
field B. Indeed it is such that the
members of an isospin pair ac-
quire the different electric charges,
the ones that we usually ascribe to
them.

► The bosons W ± acquire an
electric charge ± e that couples
them to the field A.

► The weak transitions mediated
by Z (no charge transfer, “neutral
currents”) are different from those
transmitted by the W ± . The lat-
ter ones are characterized by a
maximum parity violation because
only the left-handed leptons and
quarks are coupled to them. The
Z, however, contains not only the
W°, which is coupled to left-hand-
ed particles, but also the hyper-
electromagnetic field B that does
not distinguish the handedness in
its coupling.

So much for the description of

© ALAN W. RICHARDS.

C. N. Yang

Fundamental diagrams

(below), (a) shows the
fundamental diagram of QED.
The straight lines are electron
states ; the wavy line is a
photon state, (b) shows the
three fundamental diagrams of
QCD. The straight lines are
quark states; the wavy lines are
gluon states. Figure 3

quantum electro-weak dynamics.
The experiments have borne out
the predicted consequences as far
as they are accessible to today’s
experimentation. In particular the
mixing of equations 12 could be
verified and the angle #w deter-
mined. Several different experi-
ments lead to the same result:
sin2(?w = 0.23 ± 0.02.

The most important experimen-
tal verification is still outstanding:
the observation of the intermedi-
ate bosons. It is a similar situa-
tion to the one of Maxwell’s theory
of unification of electric and mag-
netic fields before Hertz’s experi-
ments. Woe to the theory if the
bosons are not seen when the
necessary energy and intensity for
their production is reached at
some of the accelerators under
construction!

A questionable feature of this
theory is the introduction of the
Higgs field and its somewhat arbi-
trary couplings with other fields
that are adjusted such that they
produce the correct masses. The
theory also requires the existence
of Higgs-field particles of undeter-
mined mass that have not yet
been identified. It is hoped that a
future formulation of the theory
produces the effects of the Higgs
field in a more elegant way and
gets rid of it, as QED got rid of the
vacuum filled with electrons of
negative mass!

Quantum

cnromodynamics

Running coupling constant in

OCD. The effective "charge"
Qe„ as a function of the
distance. The distance r0,
where Qe„ = 1, is of the order
of the proton radius. Figure 4

The second theory that was
structured as a parallel to quantum
electrodynamics was “quantum
chromodynamics (QCD).” It deals
with the strong interactions. Since
the discovery of the quark struc-
ture of hadrons one understands
by “strong interaction” the forces
between quarks. The nuclear
force between nucleons was the
previous candidate for that name.
Today the nuclear force is consid-
ered as a weaker derivative of the
quark-quark forces, just like the
forces between atoms are weaker
derivatives of the Coulomb forces
between the atomic constituents.

Considering the successes of
field-theoretical approaches, it is
no surprise that present attempts
to describe the interquark forces
are also structured according to
the model of quantum electrody-
— namics. Here is a dictionary of

f* the analogies:

QED

electron

charge

photon

positronium

QCD

quarks

color

gluons (massless)

Five analogs to positronium exist
in QCD because five different
types of quarks have been discov-
ered up to now. Actually QED
also predicts the existence of two
more “positroniums,” made of
each of the two heavy electrons
(p,r) and their antiparticles.

There are important differences
between these two field theories,
which mainly come from the differ-
ent nature of the charge. In QED
the charge is a scalar and remains
with the fermions. The field is un-
charged. In QCD, what acts as
the charge is a “trivalent” magni-
tude ascribed to the quarks, re-
ferred to as “color.” It is trivalent
in the same sense in which the
isotopic spin is a bivalent magni-
tude.

The color was introduced be-
cause three quarks were often
found to be in the same quantum
state. Because quarks are sup-
posed to obey the Pauli principle,
they must possess an internal
quantum number capable of as-
suming three different values.
There is a historic parallel to this:
The fact that two electrons are
found in the ground state of heli-
um has contributed to the discov-
ery of a two-valued internal quan-
tum number — the spin.

QCD assumes that the color is
the source of the field. Thus, we
again face a nonabelian situation,
but here the source is a trivalent
“spin,” whereas in quantum elec-
tro-weak dynamics we had the iso-
topic doublets of the pairs in the
table on page 81 as sources. The
consequences of QCD are also
derived from a general gauge in-
variance with respect to the ab-
stract “directions” of the trivalued
spin. We obtain again a vector
boson field whose massless quan-
ta are the gluons. The properties
of this field are analogous to the
electromagnetic field. We may
use terms such as “gluo-electric”
and “gluo-magnetic” fields. There
is one essential difference: The
fields carry color charge in a simi-
lar sense as described in expres-
sions 10. Because now we have
three quark colors a, b, c, we find
eight different types of gluons,
arising from the following emission
processes in which the quark col-
ors may change:

PARTICLES AND QUANTA

371

a b + GaB

a — * c + Gai.

b — c + Gb£

b — > a + Gba

(13)

c *■ a + Gca

c — *■ b + GcB

a — a + G0

a — a + G(,

b — * b + G0

b — b + Go

(14)

c * c + G0

c * c -)- Gg

Here GaB, etc., stands for the emit-
ted gluon that carries double color
(a, anti-b). There are eight differ-
ent gluon colors. The transitions
14 give rise to colorless gluons,
but invariance considerations
show that there are only two: G0,
Gg , just as there is only one W° in
equation 10. The fact that the
gluons carry color charge leads to
the typical nonabelian diagram in
figure 3b, which indicates that
gluons interact among each other.

A detailed description of QCD
goes beyond the aims of this arti-
cle. It may be important, howev-
er, to stress two surprising conse-
quences of this theory, of which
the second is not yet established
with certainty. The first is called
“asymptotic freedom.’’ In con-
trast to electrodynamics, the effec-
tive coupling constant decreases
when the distance decreases or
when the momentum transfer in-
creases. The coupling decreases
as the inverse of the logarithm of
the distance and, therefore, van-
ishes at infinitely close distances.
For increasingly larger distances,
however, the effective coupling
constant does not remain finite as
in QED, but seems to increase
steadily. Here again we encoun-
ter an example of a “running” cou-
pling constant but the dependence
of the effective charge Qeff on r is
very different from the one in QED
that was shown in figure 2. The
situation in QCD is sketched in fig-
ure 4. The potential energy, say,
between a quark and an antiquark
(the analog to the Coulomb energy
— e2/r between two opposite
charges) probably increases lin-
early as ar at large distances and
goes to infinity forr— ►«>.

The consequences of these re-
lations are most unusual. It fol-
lows that single quarks cannot ex-
ist as free particles. Because the
effective charge would become in-
finite at large distances, the ener-
gy necessary to isolate a quark
from its partners in a hadron would
be infinite. An isolated quark
would be surrounded by a field
that does not decrease with the
distance. Obviously, no isolated
quarks (or gluons) can exist in Na-
ture if these conclusions are con-

firmed. Only systems whose total
color charge is zero can exist in
isolation. In the spin analogy to
color, it would mean that the spins
of the constituents must be op-
posed to each other and form a
state of zero spin (singlet). In the
trivalent case, three quarks are
needed so that their colors add up
to zero, or a quark-antiquark pair.
Hence hadrons consist of either
three quarks or of a quark-anti-
quark pair, because the antiquark
has the complementary color to
the quark. (This property justifies
the use of the term “color”. The
three fundamental colors add up
to white, and so do a color and its
complementary one.)

The fact that hadrons carry no
net color charge emphasizes the
previously mentioned parallel be-
tween the nuclear force and the
forces between atoms. Atoms
are electrically neutral but when
they approach each other, their
structure is sufficiently altered that
attraction occurs through reso-
nance (Van der Waals forces) or
through formation of new quantum
states (chemical force). The
same would happen when color-
neutral nucleons approach each
other.

Here we encounter a new situa-
tion: The elementary constitu-
ents— quarks and gluons — can
only exist in bound states, never
as single free particles. It should
be noted that this paradoxical situ-
ation most probably follows (it has
not yet been proved beyond a
doubt) from a field theory that is a
generalization of QED. In the lat-
ter, of course, fermions and bo-
sons do exist as free particles;
moreover, the system of free parti-
cles is the natural limit reached
when the coupling constant goes
to zero. This limit does not exist
in QCD except for very small dis-
tances, the opposite situation to
that of free particles.

One may ask why a similar situ-
ation— the impossibility of isolated
particles — does not occur in the
case of the weak interaction,
which is also a nonabelian field
theory. The answer lies in the
fact that the symmetry of the iso-
spin space is broken by the Higgs
field at low energies (which means
low momentum transfers and large
distances) whereas the symmetry
of the color space does not seem
to be broken. Indeed, the mass
M of the field quanta (a conse-
quence of the Higgs field) pre-
vents the fields from spreading

over distances larger than h/M.
Isolated particles do not have infi-
nitely strong fields in QEWD.

Unsolved problems

The development of quantum
field theory since its inception half
a century ago is most impressive.
Today we have the means to cal-
culate electromagnetic effects with
incredible accuracy; two new field
theories were created that seem
reasonably appropriate to deal
with the strong and weak interac-
tions, the new forces of nature
that were discovered during this
half century. These forces are
more complicated than the elec-
tromagnetic ones and exhibit dif-
ferent properties, such as charge-
carrying fields, symmetries broken
by vacuum fields, and forever con-
fined particles. The fact that they
nevertheless can be described by
field theories is an indication that
the concepts of those theories
play an important role in natural
phenomena. Certainly the lan-
guage of field theory is used by
Nature. There exist today at-
tempts to bring together into one
unified theory not only the weak
and electromagnetic interactions
but also the strong ones. These
attempts use quantum electro-
weak dynamics as a model, to
bring the SU(2) doublets of the
weak forces and the SU(3) triplets
of the color variety into one super
group with new types of intermedi-
ate bosons. They are encouraged
by the fact that the strong cou-
pling constant decreases towards
higher energies so that one might
imagine a very high energy (1CT5
GeV) at which the electro-weak
and strong coupling constants
merge to one universal param-
eter. The differing values at lower
energies are again caused by sym-
metry-breaking fields of the Higgs
type.

It is by no means clear as to
whether these attempts will turn
out to be successful or not. In
this so-called “grand unification”
scheme, the Weinberg angle is no
longer arbitrary and seems to
come out close to the observed
value. It also predicts transitions
between quarks and leptons. For
example, the u quarks, each hav-
ing the charge %, end up as a
positron (charge 1) and an anti-d
quark (charge Vs). Thus a proton
(a uud combination) can decay
into a 77-° (a dd combination) and a

372

HISTORY OF PHYSICS

positron. The proton would have
a finite lifetime! Such transitions
would be very slow because they
would be mediated by some of
those new intermediate bosons
that are supposed to have masses
near the characteristic energy of
1015GeV. The lifetime of the pro-
ton should be of the order of 1 032
years. If the numerous ongoing
experiments to measure such life-
times turn out to be successful,
the ideas of field theory would win
a new victory, and a unification of
the three forces of Nature would
be in sight. This still would leave
gravity alone. The characteristic
energy at which quantum effects
become important in gravity is giv-
en by the mass of the particle pair,
whose gravitational potential ener-
gy at a distance r is equal to the
quantum energy ftc/r. It is of the
order of 1019 GeV. This is about
1000 times higher than the char-
acteristic energy of the grand unifi-
cation attempt.

There are many indications that
we understand only a partial as-
pect of what is going on. Here is
an incomplete list of questions
that are still unanswered:

► Is the renormalization proce-
dure sound? So far it can only be
carried out in successive perturba-
tion steps. Can it be applied to a
theory with an arbitrarily large cou-
pling constant? The answer to
this question may save or con-
demn field theory. A better under-
standing of the strong coupling
limit (small distances in QED, large
distances in QCD) may result in a
satisfactory solution to the prob-
lems of infinities and of confine-
ment or it may reveal fundamental
shortcomings.

► The large value of the effective
coupling constant of quantum
chromodynamics at small momen-
tum transfers causes serious prob-
lems as to the nature of the vacu-
um itself. The field fluctuations
may turn out to be very large and
may require new conceptions of
the nature of the vacuum.

► Is the present interpretation of
the electro-weak interactions cor-
rect? Do the intermediate bosons
and the Higgs field really exist?
These are questions that will soon
be answered by experiments.

► The present theories contain
arbitrary constants. Jn QED it is
the coupling constant e2/ftc at
large distances and the masses of
the different electrons. Today
three such electrons are known,
but there may be more. There is

no way visible at present to ex-
plain how .their mass values may
emerge from the field theories.
Moreover, the question remains
why there is only one value of the
electric charge (the quark charges
are simple rational fractions of it)
but several mass values seemingly
without any simple relations.

In the electro-weak interaction
there are two coupling constants
between fermions and intermedi-
ate bosons, both of the order
e2/fic. The Weinberg angle deter-
mines the ratio between the two.
Furthermore, we find arbitrary cou-
pling constants with the Higgs field
that are chosen in order to yield
the correct mass for the particles.

In QCD the situation is worse in
respect to the mass problem be-
cause we deal with many different
types of quarks, each having its
own mass value. The coupling
constant problem, however, is less
difficult in QCD, if it turns out for
sure that we deal with a running
coupling from 0 at very small dis-
tances to infinity at large ones.
Such a theory does not contain a
fixed value at large distance, like
e2/fic. But it contains length r0 (of
the order of 10“ 13 cm) at which
the running coupling constant is
near unity. We expect the com-
posite quark systems to be of that
size, and their masses to be of the
order fi/r0c, in particular when the
masses of the constituent quarks
can be negligible compared to that
mass. This is indeed the case for
those hadrons that are made of u
and d quarks. Therefore QCD
has the advantage of containing
the proton mass as a basic ingre-
dient. (In our description of Na-
ture we expect three intrinsic mag-
nitudes to appear that determine
the units of our measuring sys-
tem. Their values do not require
any explanation. These units may
well be h, c, and the length r0 as
defined above.) But there is no
indication whatsoever how the
masses of the heavier quarks are
determined by field theory. The
theory does not even allow us to
hope that the mass problem may
be answered by strong coupling
effects at small distances. As-
ymptotic freedom excludes any
such effects.

The importance of the mass
problem may be illustrated as fol-
lows. We have no explanation for
the mass of the electron, that is
for smallness of the ratio (1836)-1
between the electron mass and
the proton mass. (The latter may

be considered as the natural unit
defined by QCD.) The small value
of this ratio determines the proper-
ties of everything we see around
us. It is the precondition of molec-
ular architecture, of the fact that
the positions of atomic nuclei are
well defined within the surrounding
electron clouds. Without it there
would be no materials and no life.
We have no idea about the deeper
reasons for the smallness of that
important ratio.

► Our present view of elementary
particles is plagued by the follow-
ing problem: Nature as we know
it consists almost exclusively of u
and d quarks (the constituents of
protons and neutrons), and of ordi-
nary electrons; all important inter-
actions are mediated by photons,
intermediate bosons and gluons.
But there definitely exist higher
families of particles, such as the
heavier quarks and the heavier
electrons. These additional parti-
cles are very short-lived or give
rise to short-lived hadronic enti-
ties. They appear only under very
exceptional circumstances that are
realized during the early instances
of the big bang, perhaps in the
center of neutron stars, and at the
targets of giant accelerators. What
is their role in Nature, why do they
exist? Rabi exclaimed when he
heard of the first of those “unnec-
essary” particles, the muon:

“Who ordered them?” Again, field
theory does not seem to contain
the answer to this question. Are
they, perhaps, an indication of a
deeper internal structure within the
quarks and leptons? Are they the
excited states of systems made of
more elementary units held to-
gether by more elementary
forces? Will the quantum ladder,
the progression from atoms to nu-
clei, to nucleons and to quarks,
ever reach an end?

We will find out sooner or later
whether field theory is able to
clear up some of these outstand-
ing problems. It may be that a
very different approach will be re-
quired to solve the questions for
which field theory so far has failed
to provide answers. Nature’s lan-
guage may be much wider than
the language of field theory. We
have not yet been able to make
sense of much of what Nature
says to us.

Looking back over a lifetime of
field theory, it seems obvious that
we have learned much since 1927,
but there is a great deal more that
is still shrouded in darkness. New

PARTICLES AND QUANTA

373

ideas and new experimental facts
will be needed to shed more light
upon the deeper riddles of the ma-
terial world.

* * *

Parts of this article appeared in the pro-
ceedings of a symposium on the history of
particle physics held in May 1980 at Fermi-
tab and also in the 1979 Bernard Gregory
Lectures, CERN Report No. 80-03(1980).

References

1. There exist two interesting studies
about this subject: A. Pais, The Early
History of the Electron 1897-1947 in
Aspects of Quantum Theory, A. Salam,
E. Wigner, eds., Cambridge University
Press, 1972; S. Weinberg, Notes for a
History of Quantum Field Theory, Dae-
dalus, Fall 1977.

2. P. A. M. Dirac, Proc. Roy. Soc. 109,

642 (1926); 114, 243 (1927).

3. W. Pauli, Phys. Z. 20, 457 (1919).

4. A. Einstein, Physica 5, 330 (1925).

5. A. Pais, Rev. Mod. Phys. 51, 861(1979).

6. E. Fermi, Zeits. f. Phys. 29, 315 (1924).

7. C. V. von WeizsScker, Z. Phys. 88, 612
(1934).

8. E. J. Williams, Phys. Rev. 45, 729(1934).

9. W. Heisenberg, Z. Phys. 90, 209 (1934).

10. J. R. Oppenheimer, W. Furry, Phys.

Rev. 45, 245 (1934).

11. W. Pauli, V. F. Weisskopf, Helv. Phys.
Acta 7, 709 (1934).

12. J. R. Oppenheimer, Phys. Rev. 35, 461
(1930).

13. V. F. Weisskopf, Zeits. f. Phys. 89, 27;
90, 817 (1934).

14. F. Bloch, A. Nordsieck, Phys. Rev. 52,

54 (1937).

15. R. Serber, Phys. Rev. 48, 49 (1935).

16. E. Uehling, Phys. Rev. 48, 55 (1935).

17. H. Euler, Ann. d. Phys. V 26, 398(1936).

18. V. F. Weisskopf, Kgl. Dansk. Vid.

Selsk. 14, no. 6 (1936).

19. E. C. G. Stueckelberg, Ann. d. Phys.

21, 367 (1934).

20. E. C. G. Stueckelberg, Helv. Phys. Acta
9, 225 (1938).

21. W. Lamb, R. Retherford, Phys. Rev.

72, 241 (1947).

22. H. A. Kramers, Nuovo Cim. 15, 108(1938).

23. N. Kroll, W. Lamb, Phys. Rev. 75, 388
(1949).

24. J. B. French, V. F. Weisskopf, Phys.

Rev. 75, 1240 (1949).

25. O. Klein in New Theories in Physics,

Conf. Proc. (Warsaw, 1938), Institut In-
ternational de la Cooperation Intellec-
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26. S. Coleman, Science 206, 1290 (1979).

27. C. N. Yang, R. Mills, Phys. Rev. 96,

190 (1954). □

375

For Further Reading

The history of physics has been growing so rapidly that the biblio-
graphical notes in many of the articles in this book are out of date.
We therefore want to suggest some ways the interested reader can
venture further into this fascinating field.

There are many doorways to the history of modern physics.
Several journals regularly publish scholarly articles in the field.
Among these, Historical Studies in the Physical Sciences (Univer-
sity of California Press, Berkeley) carries by far the most articles,
all of exceptional quality, and of particular interest to physicists.
For the history of science in general, the central journal is Isis,
issued by the History of Science Society (E.F. Smith Hall, Univer-
sity of Pennsylvania, Philadelphia). Anyone interested in the field
is urged to join the Society. Members of The American Physical
Society should also join their Division of History of Physics, at no
charge, and receive its newsletter, which carries much informa-
tion on current activities such as historical sessions at meetings,
grants, and recent books. The Center for History of Physics at the
American Institute of Physics, New York City, also issues a news-
letter, available free whether or not one makes a contribution to
the Friends of the Center; this newsletter carries information
about current journal articles and projects, archival repositories,
and other news. The Center's staff and its Niels Bohr Library are
always glad to answer inquiries on historical matters. For infor-
mation on a particular historical personage, the first place to look
is the Dictionary of Scientific Biography, a fine multi volume work
available at most libraries. A thorough bibliography is in John L.
Heilbron, Bruce R. Wheaton, et al.. Literature on the History of
Physics in the 20th Century (University of California Office for
History of Science and Technology, Berkeley, 1981). An excellent
selected list is in Lars Rodseth and Stephen G. Brush, “Library
Checklist of Books and Periodicals in the History of Science,”

1 98 1 edition; copies are available from the AIP Center for History
of Physics. We list below some more recent books which make
good reading. This is only a sample of a large and rapidly growing
body of work in the history of modern physics.

Badash, Lawrence, Radioactivity in America: Growth and
Decay of a Science (Johns Hopkins University Press, Baltimore,
1979).

Bohr, Niels, Collected Works. Volumes 1-4 issued to date.
(North Holland, Amsterdam, 1972- ).

Bromberg, Joan Lisa, Fusion: Science, Politics, and the In-
vention of a New Energy Source (MIT Press, Cambridge, MA,
1982).

Brown, Laurie M., and Lillian Hoddeson, eds., The Birth of
Particle Physics (Cambridge University Press, Cambridge, 1983).

Brush, Stephen G., Statistical Physics and the Atomic Theory
of Matter, from Boyle and Newton to Landau and Onsager (Prin-
ceton University Press, Princeton, 1983).

Bunge, Mario, and William R. Shea, eds., Rutherford and
Physics at the Turn of the Century (Dawson, London; Science
History, London, 1979).

Dyson, Freeman J., Disturbing the Universe (Harper & Row,
New York, 1979).

French, A. P., ed., Einstein: A Centenary Volume (Harvard
University Press, Cambridge, MA, 1979).

Frisch, Otto R., What Little I Remember (Cambridge Uni-
versity Press, Cambridge, 1979).

Goldberg, Stanley, Understanding Relativity: Origin and
Impact of a Scientific Revolution (Birkhauser, Cambridge, MA,
1984).

Hankins, Thomas L., Sir William Rowan Hamilton (Johns
Hopkins University Press, Baltimore, 1980).

Hartcup, Gary, and Allibone, T. E., Cockcroft and the Atom
(Adam Hilger, Bristol, 1984).

Hendry, John, The Creation of Quantum Mechanics and the
Bohr-Pauli Dialogue ( Reidel, Dordrecht, 1984).

Holton, Gerald, and Yehuda Elkana, eds., Albert Einstein:
Historical and Cultural Perspectives (Princeton University Press,
Princeton, NJ, 1982).

Kargon, Robert H., The Rise of Robert Millikan: Portrait of
a Life in American Science (Cornell University Press, Ithaca, NY,
1982).

Kevles, Daniel, The Physicists: The History of a Scientific
Community in Modern America (Knopf, New York, 1978).

McCormmach, Russell, Night Thoughts of a Classical Physi-
cist (Harvard University Press, Cambridge, MA, 1982).

Mott, Nevill, ed., The Beginnings of Solid State Physics: A
Symposium... (The Royal Society, London, 1980).

Oppenheimer, Robert, Robert Oppenheimer: Letters and Re-
collections, edited by Alice Kimball Smith and Charles Weiner
(Harvard University Press, Cambridge, MA, 1980).

Pais, Abraham, "Subtle is the Lord... ”: The Science and Life
of Albert Einstein (Clarendon Press, Oxford, 1982).

Segre, Emilio, From X-rays to Quarks: Modern Physicists and
Their Discoveries (Freeman, San Francisco, 1980).

Shea, William R., ed., Otto Hahn and the Rise of Nuclear
Physics (Reidel, Boston, 1983).

Smith, Robert W., The Expanding Universe: Astronomy’s
“ Great Debate, ” 1900-1931 (Cambridge University Press, New
York, 1982).

Sopka, Katherine Russell, Quantum Physics in America,
1920-1935 (Arno, New York, 1980).

Stuewer, Roger, Nuclear Physics in Retrospect: Proceedings
of a Symposium on the 1930s (University of Minnesota Press,
Minneapolis, 1979).

Szilard, Leo, Leo Szilard: His Version of the Facts, edited by
Spencer Weart and Gertrud Weiss Szilard (MIT Press, Cam-
bridge, MA, 1978).

Truesdell, Clifford, The Tragicomical History of Thermody-
namics, 1822-1854 (Springer-Verlag, New York, 1980).

Weart, Spencer, Scientists in Power (Harvard University
Press, Cambridge, MA, 1979).

Wheaton, Bruce R., The Tiger and the Shark: Empirical
Roots of Wave-Particle Dualism (Cambridge University Press,
Cambridge, 1983).

Exploding Uranium Atoms
May Set Off Others in C

Explanation Suggested at Physics Meeting Believed
By Prof. Fermi To Be One of Several Possibilities

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